diff --git a/pylint/pyreverse/diadefslib.py b/pylint/pyreverse/diadefslib.py
index c1f14ce727..f91a89eca8 100644
--- a/pylint/pyreverse/diadefslib.py
+++ b/pylint/pyreverse/diadefslib.py
@@ -8,6 +8,7 @@
 
 import argparse
 import warnings
+from collections import defaultdict
 from collections.abc import Generator, Sequence
 from typing import Any
 
@@ -15,7 +16,7 @@
 from astroid import nodes
 from astroid.modutils import is_stdlib_module
 
-from pylint.pyreverse.diagrams import ClassDiagram, PackageDiagram
+from pylint.pyreverse.diagrams import ClassDiagram, PackageDiagram, Relationship
 from pylint.pyreverse.inspector import Linker, Project
 from pylint.pyreverse.utils import LocalsVisitor
 
@@ -272,6 +273,99 @@ def __init__(self, config: argparse.Namespace, args: Sequence[str]) -> None:
         self.config = config
         self.args = args
 
+    def _get_object_name(self, obj: Any) -> str:
+        """Get object name safely handling both title attributes and strings.
+
+        :param obj: Object to get name from
+        :return: Object name/title
+        :rtype: str
+        """
+        return obj.title if hasattr(obj, "title") else str(obj)
+
+    def _process_relationship(
+        self, relationship: Relationship, unique_classes: dict[str, Any], obj: Any
+    ) -> None:
+        """Process a single relationship for deduplication.
+
+        :param relationship: Relationship to process
+        :param unique_classes: Dict of unique classes
+        :param obj: Current object being processed
+        """
+        if relationship.from_object == obj:
+            relationship.from_object = unique_classes[obj.node.qname()]
+        if relationship.to_object == obj:
+            relationship.to_object = unique_classes[obj.node.qname()]
+
+    def _process_class_relationships(
+        self, diagram: ClassDiagram, obj: Any, unique_classes: dict[str, Any]
+    ) -> None:
+        """Merge relationships for a class.
+
+        :param diagram: Current diagram
+        :param obj: Object whose relationships to process
+        :param unique_classes: Dict of unique classes
+        """
+        for rel_type in ("specialization", "association", "aggregation"):
+            for rel in diagram.get_relationships(rel_type):
+                self._process_relationship(rel, unique_classes, obj)
+
+    def deduplicate_classes(self, diagrams: list[ClassDiagram]) -> list[ClassDiagram]:
+        """Remove duplicate classes from diagrams."""
+        for diagram in diagrams:
+            # Track unique classes by qualified name
+            unique_classes: dict[str, Any] = {}
+            duplicate_classes: Any = set()
+
+            # First pass - identify duplicates
+            for obj in diagram.objects:
+                qname = obj.node.qname()
+                if qname in unique_classes:
+                    duplicate_classes.add(obj)
+                    self._process_class_relationships(diagram, obj, unique_classes)
+                else:
+                    unique_classes[qname] = obj
+
+            # Second pass - filter out duplicates
+            diagram.objects = [
+                obj for obj in diagram.objects if obj not in duplicate_classes
+            ]
+
+        return diagrams
+
+    def _process_relationship_type(
+        self,
+        rel_list: list[Relationship],
+        seen: set[tuple[str, str, str, Any | None]],
+        unique_rels: dict[str, list[Relationship]],
+        rel_name: str,
+    ) -> None:
+        """Process a list of relationships of a single type.
+
+        :param rel_list: List of relationships to process
+        :param seen: Set of seen relationships
+        :param unique_rels: Dict to store unique relationships
+        :param rel_name: Name of relationship type
+        """
+        for rel in rel_list:
+            key = (
+                self._get_object_name(rel.from_object),
+                self._get_object_name(rel.to_object),
+                type(rel).__name__,
+                getattr(rel, "name", None),
+            )
+            if key not in seen:
+                seen.add(key)
+                unique_rels[rel_name].append(rel)
+
+    def deduplicate_relationships(self, diagram: ClassDiagram) -> None:
+        """Remove duplicate relationships between objects."""
+        seen: set[tuple[str, str, str, Any | None]] = set()
+        unique_rels: dict[str, list[Relationship]] = defaultdict(list)
+        for rel_name, rel_list in diagram.relationships.items():
+            self._process_relationship_type(rel_list, seen, unique_rels, rel_name)
+
+        diagram.relationships = dict(unique_rels)
+
     def get_diadefs(self, project: Project, linker: Linker) -> list[ClassDiagram]:
         """Get the diagram's configuration data.
 
@@ -292,4 +386,5 @@ def get_diadefs(self, project: Project, linker: Linker) -> list[ClassDiagram]:
             diagrams = DefaultDiadefGenerator(linker, self).visit(project)
         for diagram in diagrams:
             diagram.extract_relationships()
-        return diagrams
+            self.deduplicate_relationships(diagram)
+        return self.deduplicate_classes(diagrams)
diff --git a/tests/pyreverse/functional/class_diagrams/aggregation/class_attribute_duplicate.mmd b/tests/pyreverse/functional/class_diagrams/aggregation/class_attribute_duplicate.mmd
new file mode 100644
index 0000000000..5e451ec3af
--- /dev/null
+++ b/tests/pyreverse/functional/class_diagrams/aggregation/class_attribute_duplicate.mmd
@@ -0,0 +1,9 @@
+classDiagram
+  class A {
+    var : int
+  }
+  class B {
+    a_obj
+    func()
+  }
+  A --* B : a_obj
diff --git a/tests/pyreverse/functional/class_diagrams/aggregation/class_attribute_duplicate.py b/tests/pyreverse/functional/class_diagrams/aggregation/class_attribute_duplicate.py
new file mode 100644
index 0000000000..eccd0aee86
--- /dev/null
+++ b/tests/pyreverse/functional/class_diagrams/aggregation/class_attribute_duplicate.py
@@ -0,0 +1,13 @@
+# Test for issue #9267
+class A:
+    def __init__(self) -> None:
+        self.var = 2
+
+
+class B:
+    def __init__(self) -> None:
+        self.a_obj = A()
+
+    def func(self):
+        self.a_obj = A()
+        self.a_obj = A()