diff --git a/DESCRIPTION b/DESCRIPTION
index b83eaeae..a7f58d5d 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -84,6 +84,7 @@ Collate:
     'DISTANCES-sdtw.R'
     'GENERICS-cvi.R'
     'S4-Distmat.R'
+    'S4-DistmatLowerTriangular.R'
     'S4-PairTracker.R'
     'S4-SparseDistmat.R'
     'S4-tsclustFamily.R'
diff --git a/NAMESPACE b/NAMESPACE
index 22569d42..2ddc3d81 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -6,6 +6,7 @@ S3method(as.data.frame,pairdist)
 S3method(as.matrix,crossdist)
 S3method(as.matrix,pairdist)
 S3method(base::dim,Distmat)
+S3method(base::dim,DistmatLowerTriangular)
 S3method(base::dim,SparseDistmat)
 S3method(cl_class_ids,TSClusters)
 S3method(cl_membership,TSClusters)
@@ -105,6 +106,7 @@ importFrom(ggplot2,theme_bw)
 importFrom(ggrepel,geom_label_repel)
 importFrom(graphics,plot)
 importFrom(methods,S3Part)
+importFrom(methods,as)
 importFrom(methods,callNextMethod)
 importFrom(methods,initialize)
 importFrom(methods,is)
diff --git a/R/CLUSTERING-ddist2.R b/R/CLUSTERING-ddist2.R
index 73c904c9..7beddeaf 100644
--- a/R/CLUSTERING-ddist2.R
+++ b/R/CLUSTERING-ddist2.R
@@ -143,7 +143,7 @@ parallel_symmetric <- function(d_desc, ids, x, distance, dots) {
 #' @importFrom proxy dist
 #' @importFrom proxy pr_DB
 #'
-ddist2 <- function(distance, control) {
+ddist2 <- function(distance, control, lower_triangular_only = FALSE) {
     # I need to re-register any custom distances in each parallel worker
     dist_entry <- proxy::pr_DB$get_entry(distance)
     symmetric <- isTRUE(control$symmetric)
@@ -175,20 +175,23 @@ ddist2 <- function(distance, control) {
             return(ret(use_distmat(control$distmat, x, centroids)))
         }
 
-        dots <- get_dots(dist_entry, x, centroids, ...)
+        dots <- get_dots(dist_entry, x, centroids, ..., lower_triangular_only = lower_triangular_only)
 
         if (!dist_entry$loop) {
             # CUSTOM LOOP, LET THEM HANDLE OPTIMIZATIONS
-            dm <- base::as.matrix(quoted_call(
+            dm <- quoted_call(
                 proxy::dist, x = x, y = centroids, method = distance, dots = dots
-            ))
+            )
 
             if (isTRUE(dots$pairwise)) {
                 dim(dm) <- NULL
                 return(ret(dm, class = "pairdist"))
             }
+            else if (lower_triangular_only && inherits(dm, "dist")) {
+                return(ret(dm, class = "dist", Size = length(x)))
+            }
             else {
-                return(ret(dm, class = "crossdist"))
+                return(ret(base::as.matrix(dm), class = "crossdist"))
             }
         }
 
@@ -237,11 +240,16 @@ ddist2 <- function(distance, control) {
             }
             else if (!multiple_workers) {
                 # WHOLE SYMMETRIC DISTMAT WITHOUT CUSTOM LOOP OR USING SEQUENTIAL proxy LOOP
-                dm <- base::as.matrix(quoted_call(
+                dm <- quoted_call(
                     proxy::dist, x = x, y = NULL, method = distance, dots = dots
-                ))
+                )
 
-                return(ret(dm, class = "crossdist"))
+                if (lower_triangular_only && inherits(dm, "dist")) {
+                    return(ret(dm, class = "dist", Size = length(x)))
+                }
+                else {
+                    return(ret(base::as.matrix(dm), class = "crossdist"))
+                }
             }
         }
 
diff --git a/R/CLUSTERING-tsclust.R b/R/CLUSTERING-tsclust.R
index c5ad1d89..40b30679 100644
--- a/R/CLUSTERING-tsclust.R
+++ b/R/CLUSTERING-tsclust.R
@@ -3,16 +3,31 @@
 # ==================================================================================================
 
 # Get an appropriate distance matrix object for internal use with PAM/FCMdd centroids
+#' @importFrom methods as
 pam_distmat <- function(series, control, distance, cent_char, family, args, trace) {
     distmat <- control$distmat
     distmat_provided <- FALSE
 
     if (!is.null(distmat)) {
-        if (nrow(distmat) != length(series) || ncol(distmat) != length(series))
-            stop("Dimensions of provided cross-distance matrix don't correspond ",
-                 "to length of provided data")
-        # see S4-Distmat.R
-        if (!inherits(distmat, "Distmat")) distmat <- Distmat$new(distmat = distmat)
+        if (inherits(distmat, "dist")) {
+            n <- attr(distmat, "Size")
+            if (n != length(series))
+                stop("Dimensions of provided cross-distance matrix don't correspond ",
+                     "to length of provided data")
+
+            # see S4-Distmat.R
+            if (!inherits(distmat, "Distmat"))
+                distmat <- DistmatLowerTriangular$new(distmat = distmat)
+        }
+        else {
+            if (nrow(distmat) != length(series) || ncol(distmat) != length(series))
+                stop("Dimensions of provided cross-distance matrix don't correspond ",
+                     "to length of provided data")
+
+            # see S4-Distmat.R
+            if (!inherits(distmat, "Distmat")) distmat <- Distmat$new(distmat = distmat)
+        }
+
         distmat_provided <- TRUE
         if (trace) cat("\n\tDistance matrix provided...\n\n") # nocov
     }
@@ -20,13 +35,21 @@ pam_distmat <- function(series, control, distance, cent_char, family, args, trac
         if (distance == "dtw_lb")
             warning("Using dtw_lb with control$pam.precompute = TRUE is not advised.") # nocov
         if (trace) cat("\n\tPrecomputing distance matrix...\n\n")
-        # see S4-Distmat.R
-        distmat <- Distmat$new(distmat = quoted_call(
-            family@dist,
-            x = series,
-            centroids = NULL,
-            dots = args$dist
-        ))
+
+        if (control$symmetric) {
+            distfun <- ddist2(distance, control, lower_triangular_only = TRUE)
+            distmat <- methods::as(quoted_call(distfun, x = series, centroids = NULL, dots = args$dist),
+                                   "Distmat")
+        }
+        else {
+            # see S4-Distmat.R
+            distmat <- Distmat$new(distmat = quoted_call(
+                family@dist,
+                x = series,
+                centroids = NULL,
+                dots = args$dist
+            ))
+        }
     }
     else {
         if (isTRUE(control$pam.sparse) && distance != "dtw_lb") {
diff --git a/R/S4-DistmatLowerTriangular.R b/R/S4-DistmatLowerTriangular.R
new file mode 100644
index 00000000..1f81f043
--- /dev/null
+++ b/R/S4-DistmatLowerTriangular.R
@@ -0,0 +1,129 @@
+lower_triangular_index <- function(i, j, n, diagonal) {
+    stopifnot(i > 0L, i <= n, j > 0L, j <= i)
+
+    i <- i - 1L
+    j <- j - 1L
+
+    adjustment <- if (diagonal) {
+        0L
+    }
+    else {
+        Reduce(x = 0L:j, init = 0L, f = function(a, b) { a + b + 1L })
+    }
+
+    i + j * n - adjustment + 1L
+}
+
+#' Distance matrix's lower triangular
+#'
+#' Reference class that is used internally for PAM centroids when `pam.precompute = TRUE` and
+#' `pam.sparse = FALSE`. It contains [Distmat-class].
+#'
+#' @include S4-Distmat.R
+#' @importFrom methods setRefClass
+#'
+#' @field distmat The lower triangular.
+#'
+#' @keywords internal
+#'
+DistmatLowerTriangular <- methods::setRefClass(
+    "DistmatLowerTriangular",
+    contains = "Distmat",
+    fields = list(
+        distmat = "ANY"
+    ),
+    methods = list(
+        initialize = function(..., distmat) {
+            "Initialization based on needed parameters"
+
+            if (missing(distmat)) {
+                stop("distmat must be provided for this class.")
+            }
+            else if (!inherits(distmat, "dist")) {
+                stop("distmat must be a 'dist' object.")
+            }
+
+            callSuper(..., distmat = distmat)
+            # return
+            invisible(NULL)
+        }
+    )
+)
+
+#' Generics for `DistmatLowerTriangular`
+#'
+#' Generics with methods for [DistmatLowerTriangular-class].
+#'
+#' @name DistmatLowerTriangular-generics
+#' @rdname DistmatLowerTriangular-generics
+#' @keywords internal
+#' @importFrom methods setMethod
+#'
+NULL
+
+#' @rdname DistmatLowerTriangular-generics
+#' @aliases show,DistmatLowerTriangular
+#' @importFrom methods show
+#'
+#' @param object A [DistmatLowerTriangular-class] object.
+#'
+setMethod("show", "DistmatLowerTriangular", function(object) { methods::show(object$distmat) }) # nocov
+
+#' @rdname DistmatLowerTriangular-generics
+#' @aliases [,DistmatLowerTriangular,ANY,ANY,ANY
+#'
+#' @param x A [DistmatLowerTriangular-class] object.
+#' @param i Row indices.
+#' @param j Column indices.
+#' @param ... Ignored.
+#'
+setMethod(`[`, "DistmatLowerTriangular", function(x, i, j, ...) {
+    if (missing(j)) {
+        stopifnot(inherits(i, "matrix"), ncol(i) == 2L)
+        j <- i[, 2L]
+        i <- i[, 1L]
+        drop <- TRUE
+    }
+    else {
+        out_dim <- c(length(i), length(j))
+        out_dimnames <- list(i, j)
+        combinations <- expand.grid(i = i, j = j)
+        i <- combinations$i
+        j <- combinations$j
+        drop <- FALSE
+
+    }
+
+    n <- attr(x$distmat, "Size")
+    diagonal <- isTRUE(attr(x$distmat, "Diag"))
+    entries <- mapply(i, j, FUN = function(i, j) {
+        if (!diagonal && i == j) {
+            0
+        }
+        else if (j > i) {
+            x$distmat[lower_triangular_index(j, i, n, diagonal)]
+        }
+        else {
+            x$distmat[lower_triangular_index(i, j, n, diagonal)]
+        }
+    })
+
+    if (drop) {
+        entries
+    }
+    else {
+        dim(entries) <- out_dim
+        dimnames(entries) <- out_dimnames
+        entries
+    }
+})
+
+#' @exportS3Method base::dim
+dim.DistmatLowerTriangular <- function(x) { rep(attr(x$distmat, "Size"), 2L) } # nocov
+
+methods::setOldClass("dist")
+methods::setOldClass("crossdist")
+
+setAs("matrix", "Distmat", function(from) { Distmat$new(distmat = from) })
+setAs("crossdist", "Distmat", function(from) { Distmat$new(distmat = from) })
+setAs("dist", "Distmat", function(from) { DistmatLowerTriangular$new(distmat = from) })
diff --git a/R/S4-tsclustFamily.R b/R/S4-tsclustFamily.R
index d4c0bf5b..6e81f869 100644
--- a/R/S4-tsclustFamily.R
+++ b/R/S4-tsclustFamily.R
@@ -143,10 +143,14 @@ setMethod("initialize", "tsclustFamily",
               if (!missing(allcent)) {
                   if (is.character(allcent)) {
                       if (allcent %in% c("pam", "fcmdd")) {
-                          if (!is.null(control$distmat) && !inherits(control$distmat, "Distmat"))
-                              control$distmat <- Distmat$new( # see S4-Distmat.R
-                                  distmat = base::as.matrix(control$distmat)
-                              )
+                          if (!is.null(control$distmat) && !inherits(control$distmat, "Distmat")) {
+                              control$distmat <- if (inherits(control$distmat, "dist")) {
+                                  DistmatLowerTriangular$new(distmat = control$distmat)
+                              }
+                              else {
+                                  Distmat$new(distmat = control$distmat)
+                              }
+                          }
                       }
                       allcent <- all_cent2(allcent, control)
                   }
diff --git a/man/DistmatLowerTriangular-class.Rd b/man/DistmatLowerTriangular-class.Rd
new file mode 100644
index 00000000..3a97c4de
--- /dev/null
+++ b/man/DistmatLowerTriangular-class.Rd
@@ -0,0 +1,24 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/S4-DistmatLowerTriangular.R
+\docType{class}
+\name{DistmatLowerTriangular-class}
+\alias{DistmatLowerTriangular-class}
+\alias{DistmatLowerTriangular}
+\title{Distance matrix's lower triangular}
+\description{
+Reference class that is used internally for PAM centroids when \code{pam.precompute = TRUE} and
+\code{pam.sparse = FALSE}. It contains \linkS4class{Distmat}.
+}
+\section{Fields}{
+
+\describe{
+\item{\code{distmat}}{The lower triangular.}
+}}
+
+\section{Methods}{
+
+\describe{
+\item{\code{initialize(..., distmat, series, distance, control, error.check = TRUE)}}{Initialization based on needed parameters}
+}}
+
+\keyword{internal}
diff --git a/man/DistmatLowerTriangular-generics.Rd b/man/DistmatLowerTriangular-generics.Rd
new file mode 100644
index 00000000..2aba74c3
--- /dev/null
+++ b/man/DistmatLowerTriangular-generics.Rd
@@ -0,0 +1,29 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/S4-DistmatLowerTriangular.R
+\name{DistmatLowerTriangular-generics}
+\alias{DistmatLowerTriangular-generics}
+\alias{show,DistmatLowerTriangular-method}
+\alias{show,DistmatLowerTriangular}
+\alias{[,DistmatLowerTriangular,ANY,ANY,ANY-method}
+\alias{[,DistmatLowerTriangular,ANY,ANY,ANY}
+\title{Generics for \code{DistmatLowerTriangular}}
+\usage{
+\S4method{show}{DistmatLowerTriangular}(object)
+
+\S4method{[}{DistmatLowerTriangular,ANY,ANY,ANY}(x, i, j, ..., drop = TRUE)
+}
+\arguments{
+\item{object}{A \linkS4class{DistmatLowerTriangular} object.}
+
+\item{x}{A \linkS4class{DistmatLowerTriangular} object.}
+
+\item{i}{Row indices.}
+
+\item{j}{Column indices.}
+
+\item{...}{Ignored.}
+}
+\description{
+Generics with methods for \linkS4class{DistmatLowerTriangular}.
+}
+\keyword{internal}
diff --git a/tests/testthat/integration/custom-dist.R b/tests/testthat/integration/custom-dist.R
index d10bae9a..f5e4f349 100644
--- a/tests/testthat/integration/custom-dist.R
+++ b/tests/testthat/integration/custom-dist.R
@@ -44,6 +44,8 @@ test_that("Calling tsclust after registering a custom distance works as expected
     ## just for expect below
     pc_ndtw@control$symmetric <- TRUE
     pc_ndtw@call <- pc_ndtw_sym@call <- as.call(list("foo", bar = 1))
+    pc_ndtw@control$distmat <- pc_ndtw@distmat <- as.matrix(pc_ndtw@distmat)
+    pc_ndtw_sym@control$distmat <- pc_ndtw_sym@distmat <- as.matrix(pc_ndtw_sym@distmat)
 
     expect_identical(pc_ndtw, pc_ndtw_sym)
 
diff --git a/tests/testthat/rds/pc_ndtw.rds b/tests/testthat/rds/pc_ndtw.rds
index de5bf6ff..20a4f487 100644
Binary files a/tests/testthat/rds/pc_ndtw.rds and b/tests/testthat/rds/pc_ndtw.rds differ
diff --git a/tests/testthat/rds/pc_ndtw_sym.rds b/tests/testthat/rds/pc_ndtw_sym.rds
index de5bf6ff..20a4f487 100644
Binary files a/tests/testthat/rds/pc_ndtw_sym.rds and b/tests/testthat/rds/pc_ndtw_sym.rds differ