diff --git a/Modules/IO/GDCM/include/itkGDCMSeriesFileNames.h b/Modules/IO/GDCM/include/itkGDCMSeriesFileNames.h
index b1c0659d6f4..4015f2b38f6 100644
--- a/Modules/IO/GDCM/include/itkGDCMSeriesFileNames.h
+++ b/Modules/IO/GDCM/include/itkGDCMSeriesFileNames.h
@@ -42,7 +42,8 @@ namespace itk
  *      orientation), an exception is thrown by default; see
  *      FailOnAmbiguousOrdering. When FailOnAmbiguousOrdering is false, the
  *      ordering falls back to 'Instance Number' when unique, else to
- *      lexicographic filename order.
+ *      lexicographic filename order (and in either case, DidUseAmbiguousOrdering
+ *      is set to true).
  *
  *  If multiple volumes are being grouped as a single series for your
  *    DICOM objects, you may want to try calling SetUseSeriesDetails(true)
@@ -172,7 +173,7 @@ class ITKIOGDCM_EXPORT GDCMSeriesFileNames : public ProcessObject
   void
   AddSeriesRestriction(const std::string & tag);
 
-  /** Throw an exception when a series cannot be ordered geometrically by
+  /** When true, throw an exception when a series cannot be ordered geometrically by
    * gdcm::IPPSorter (duplicate ImagePositionPatient, inconsistent
    * orientation). When false, fall back to the legacy SerieHelper
    * heuristics: Instance Number when unique, else lexicographic filename
@@ -184,6 +185,11 @@ class ITKIOGDCM_EXPORT GDCMSeriesFileNames : public ProcessObject
   itkBooleanMacro(FailOnAmbiguousOrdering);
   /** @ITKEndGrouping */
 
+  /** If ambiguous ordering is encountered, this is set to true. */
+  /** @ITKStartGrouping */
+  itkGetConstMacro(DidUseAmbiguousOrdering, bool);
+  /** @ITKEndGrouping */
+
   /** No effect with the gdcm::Scanner backend (retained for source
    *  compatibility). Series enumeration reads only the grouping and
    *  ordering tags, so sequences are never parsed during the scan.
@@ -256,6 +262,7 @@ class ITKIOGDCM_EXPORT GDCMSeriesFileNames : public ProcessObject
 
   bool m_UseSeriesDetails = false;
   bool m_FailOnAmbiguousOrdering = true;
+  bool m_DidUseAmbiguousOrdering = false;
   bool m_Recursive = false;
   bool m_LoadSequences = false;
   bool m_LoadPrivateTags = false;
diff --git a/Modules/IO/GDCM/src/itkGDCMSeriesFileNames.cxx b/Modules/IO/GDCM/src/itkGDCMSeriesFileNames.cxx
index 1aff70081ca..a1356007ebb 100644
--- a/Modules/IO/GDCM/src/itkGDCMSeriesFileNames.cxx
+++ b/Modules/IO/GDCM/src/itkGDCMSeriesFileNames.cxx
@@ -218,7 +218,12 @@ GDCMSeriesFileNames::OrderSeries(SeriesEntry & entry)
   // acquisitions (see issue #6468).
   gdcm::IPPSorter sorter;
   sorter.SetComputeZSpacing(false);
-  if (sorter.Sort(entry.Files))
+  bool wasSortingAchieved = sorter.Sort(entry.Files);
+
+  // Set a public flag so that callers know this fallback occurred, and can show a warning.
+  m_DidUseAmbiguousOrdering = !wasSortingAchieved;
+
+  if (wasSortingAchieved)
   {
     entry.Files = sorter.GetFilenames();
     entry.Ordered = true;
@@ -230,6 +235,7 @@ GDCMSeriesFileNames::OrderSeries(SeriesEntry & entry)
                       "orientation, see issue #6468). Set FailOnAmbiguousOrdering to false to accept the legacy "
                       "non-standard ordering heuristics.");
   }
+
   // Legacy SerieHelper heuristics (Instance Number, then lexicographic),
   // kept only for determinism and backward compatibility: an untrustworthy,
   // non-standard hack whose output should not be trusted.
@@ -412,6 +418,7 @@ GDCMSeriesFileNames::PrintSelf(std::ostream & os, Indent indent) const
 
   itkPrintSelfBooleanMacro(UseSeriesDetails);
   itkPrintSelfBooleanMacro(FailOnAmbiguousOrdering);
+  itkPrintSelfBooleanMacro(DidUseAmbiguousOrdering);
   itkPrintSelfBooleanMacro(Recursive);
   itkPrintSelfBooleanMacro(LoadSequences);
   itkPrintSelfBooleanMacro(LoadPrivateTags);