How did Mordred betray King Arthur?

Mordred betrayed King Arthur by usurping his throne and seeking to take control of Camelot. After Arthur left to fight in a battle, Mordred took advantage of his absence by declaring himself king and attempting to seduce Arthur's queen, Guinevere. This act of treachery ultimately led to the downfall of Arthur's reign and the catastrophic battle of Camlann, where Arthur and Mordred faced each other. Mordred's betrayal is often depicted as a culmination of personal ambition and a deep-seated conflict within Arthur's court.