Brody Jenner betrays the whole Kardashian family!

Brody Jenner may have been too busy to attend his step-sister's wedding last month, but he cleared the decks to attend her ex-boyfriend's nuptials.

Reggie Bush tied the knot in grand style -- though still short of Versaillis -- at the Grand Del Mar in San Diego ... rated the #1 hotel in America by TripAdvisor's.

It's no secret ... there's no love lost between Kim Kardashian and Reggie, so it's pretty interesting Brody chose to go. 

Oh the horror, he went to a wedding!