diff --git a/docs/user/api/v3.rst b/docs/user/api/v3.rst
index dab6bf10e19..a76858498fe 100644
--- a/docs/user/api/v3.rst
+++ b/docs/user/api/v3.rst
@@ -308,12 +308,21 @@ Project details
 
          * **expand** (*string*) -- Add additional fields in the response.
            Allowed values are: ``organization``.
+           We used to return a full organization object in the response,
+           due to privacy concerns, now we return only the slug of the organization.
+           If you need to get the full organization object, you can use the organization endpoint with the slug.
 
     .. note::
 
        The ``single_version`` attribute is deprecated,
        use ``versioning_scheme`` instead.
 
+    .. note::
+
+       Previously, ``translation_of`` and ``subproject_of`` returned a full project object,
+       due to privacy concerns, now they return only the slug of the project.
+       If you need to get the full project object, you can use the project endpoint with the slug.
+
 Project create
 ++++++++++++++
 
diff --git a/readthedocs/api/v3/serializers.py b/readthedocs/api/v3/serializers.py
index b271cf255fd..c0452ef99df 100644
--- a/readthedocs/api/v3/serializers.py
+++ b/readthedocs/api/v3/serializers.py
@@ -736,6 +736,26 @@ def get_admin(self, obj):
         return AdminPermission.is_admin(user, obj)
 
 
+class RelatedProjectSerializer(serializers.ModelSerializer):
+
+    """
+    Stripped version of the ProjectSerializer to be used when including related projects.
+
+    This serializer is used to avoid leaking information about a private project through
+    a public project. Instead of checking if user has access to the project,
+    we just show the slug.
+    """
+
+    _links = ProjectLinksSerializer(source="*")
+
+    class Meta:
+        model = Project
+        fields = [
+            "slug",
+            "_links",
+        ]
+
+
 class ProjectSerializer(FlexFieldsModelSerializer):
 
     """
@@ -766,6 +786,8 @@ class ProjectSerializer(FlexFieldsModelSerializer):
     created = serializers.DateTimeField(source="pub_date")
     modified = serializers.DateTimeField(source="modified_date")
 
+    related_project_serializer = RelatedProjectSerializer
+
     class Meta:
         model = Project
         fields = [
@@ -812,7 +834,7 @@ class Meta:
             # Users can use the /api/v3/organizations/ endpoint to get more information
             # about the organization.
             "organization": (
-                "readthedocs.api.v3.serializers.RestrictedOrganizationSerializer",
+                "readthedocs.api.v3.serializers.RelatedOrganizationSerializer",
                 # NOTE: we cannot have a Project with multiple organizations.
                 {"source": "organizations.first"},
             ),
@@ -846,13 +868,16 @@ def get_homepage(self, obj):
 
     def get_translation_of(self, obj):
         if obj.main_language_project:
-            return self.__class__(obj.main_language_project).data
+            # Since the related project can be private, we use a restricted serializer.
+            return self.related_project_serializer(obj.main_language_project).data
+        return None
 
     def get_subproject_of(self, obj):
-        try:
-            return self.__class__(obj.superprojects.first().parent).data
-        except Exception:
-            return None
+        parent_relationship = obj.superprojects.first()
+        if parent_relationship:
+            # Since the related project can be private, we use a restricted serializer.
+            return self.related_project_serializer(parent_relationship.parent).data
+        return None
 
 
 class SubprojectCreateSerializer(FlexFieldsModelSerializer):
@@ -1230,7 +1255,7 @@ class Meta:
         )
 
 
-class RestrictedOrganizationSerializer(serializers.ModelSerializer):
+class RelatedOrganizationSerializer(serializers.ModelSerializer):
 
     """
     Stripped version of the OrganizationSerializer to be used when listing projects.
@@ -1244,7 +1269,6 @@ class RestrictedOrganizationSerializer(serializers.ModelSerializer):
     class Meta:
         model = Organization
         fields = (
-            "name",
             "slug",
             "_links",
         )
diff --git a/readthedocs/proxito/tests/test_hosting.py b/readthedocs/proxito/tests/test_hosting.py
index a990fe2a984..3b23f3b71db 100644
--- a/readthedocs/proxito/tests/test_hosting.py
+++ b/readthedocs/proxito/tests/test_hosting.py
@@ -843,7 +843,7 @@ def test_number_of_queries_url_subproject(self):
                 active=True,
             )
 
-        with self.assertNumQueries(31):
+        with self.assertNumQueries(26):
             r = self.client.get(
                 reverse("proxito_readthedocs_docs_addons"),
                 {
@@ -869,7 +869,7 @@ def test_number_of_queries_url_translations(self):
                 language=language,
             )
 
-        with self.assertNumQueries(58):
+        with self.assertNumQueries(42):
             r = self.client.get(
                 reverse("proxito_readthedocs_docs_addons"),
                 {
diff --git a/readthedocs/proxito/views/hosting.py b/readthedocs/proxito/views/hosting.py
index 933f359fbec..3299419c991 100644
--- a/readthedocs/proxito/views/hosting.py
+++ b/readthedocs/proxito/views/hosting.py
@@ -16,6 +16,7 @@
 from readthedocs.api.v3.serializers import (
     BuildSerializer,
     ProjectSerializer,
+    RelatedProjectSerializer,
     VersionSerializer,
 )
 from readthedocs.builds.constants import BUILD_STATE_FINISHED, LATEST
@@ -245,7 +246,13 @@ def __init__(self, *args, **kwargs):
 # on El Proxito.
 #
 # See https://github.com/readthedocs/readthedocs-ops/issues/1323
+class RelatedProjectSerializerNoLinks(NoLinksMixin, RelatedProjectSerializer):
+    pass
+
+
 class ProjectSerializerNoLinks(NoLinksMixin, ProjectSerializer):
+    related_project_serializer = RelatedProjectSerializerNoLinks
+
     def __init__(self, *args, **kwargs):
         resolver = kwargs.pop("resolver", Resolver())
         super().__init__(