diff --git a/git/diff.py b/git/diff.py
index aba1a108..e5db4a8f 100644
--- a/git/diff.py
+++ b/git/diff.py
@@ -8,6 +8,7 @@ import re
 from git.cmd import handle_process_output
 from git.compat import defenc
 from git.util import finalize_process, hex_to_bin
+from git.exc import GitCommandError
 
 from .objects.blob import Blob
 from .objects.util import mode_str_to_int
@@ -154,6 +155,10 @@ class Diffable:
             args.append("-M")
 
         if create_patch:
+            # When creating patches, we need to bypass external diff settings
+            # as external diff tools don't produce the unified diff format we can parse
+            args.append("-c")
+            args.append("diff.external=")  # Override to empty string to disable external diff
             args.append("-p")
         else:
             args.append("--raw")
diff --git a/reproduce_issue.py b/reproduce_issue.py
new file mode 100644
index 00000000..1b459e77
--- /dev/null
+++ b/reproduce_issue.py
@@ -0,0 +1,75 @@
+from git import Repo
+import tempfile
+import os
+
+# Create a temporary repo
+repo_dir = tempfile.mkdtemp()
+print(f"Using repo dir: {repo_dir}")
+os.chdir(repo_dir)
+
+# Initialize repo
+repo = Repo.init(repo_dir)
+
+# Create a test file
+test_file = os.path.join(repo_dir, "test.txt")
+with open(test_file, "w") as f:
+    f.write("hello world\n")
+
+# Add and commit
+repo.git.add(test_file)
+repo.index.commit("initial commit")
+
+# Modify the file
+with open(test_file, "w") as f:
+    f.write("hello world\nmodified line\n")
+
+print("Without create_patch:")
+print(repo.index.diff("HEAD"))
+print(repo.index.diff(None))
+
+print("\nWith create_patch:")
+print("HEAD vs HEAD^:", repo.head.commit.diff("HEAD^", create_patch=True))  # tree vs tree
+print("index vs HEAD:", repo.index.diff("HEAD", create_patch=True))        # index vs tree  
+print("index vs working:", repo.index.diff(None, create_patch=True))      # index vs working tree
+print("working tree vs HEAD:", repo.head.commit.diff(None, create_patch=True)) # working tree vs tree
+
+# Set external diff
+with repo.config_writer(config_level="repository") as writer:
+    writer.set_value("diff", "external", "bogus_diff_engine")
+
+print("\n=== WITH EXTERNAL DIFF ===")
+print("Without create_patch:")
+try:
+    print("HEAD vs HEAD^:", repo.head.commit.diff("HEAD^"))  # tree vs tree
+except Exception as e:
+    print("HEAD vs HEAD^: ERROR -", e)
+try:
+    print("index vs HEAD:", repo.index.diff("HEAD"))        # index vs tree  
+except Exception as e:
+    print("index vs HEAD: ERROR -", e)
+try:
+    print("index vs working:", repo.index.diff(None))      # index vs working tree
+except Exception as e:
+    print("index vs working: ERROR -", e)
+try:
+    print("working tree vs HEAD:", repo.head.commit.diff(None)) # working tree vs tree
+except Exception as e:
+    print("working tree vs HEAD: ERROR -", e)
+
+print("\nWith create_patch:")
+try:
+    print("HEAD vs HEAD^:", repo.head.commit.diff("HEAD^", create_patch=True))  # tree vs tree
+except Exception as e:
+    print("HEAD vs HEAD^: ERROR -", e)
+try:
+    print("index vs HEAD:", repo.index.diff("HEAD", create_patch=True))        # index vs tree  
+except Exception as e:
+    print("index vs HEAD: ERROR -", e)
+try:
+    print("index vs working:", repo.index.diff(None, create_patch=True))      # index vs working tree
+except Exception as e:
+    print("index vs working: ERROR -", e)
+try:
+    print("working tree vs HEAD:", repo.head.commit.diff(None, create_patch=True)) # working tree vs tree
+except Exception as e:
+    print("working tree vs HEAD: ERROR -", e)
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