This Bible contradiction is from the Skeptic's Annotated Bible.

Verses

In the twelfth year of Joram.

2 Kings 8:25 View context

In the twelfth year of Joram the son of Ahab king of Israel did Ahaziah the son of Jehoram king of Judah begin to reign.

In the eleventh year of Joram.

2 Kings 9:29 View context

And in the eleventh year of Joram the son of Ahab began Ahaziah to reign over Judah.