Britney Spears wore a backless Halston Heritage dress last night to join her fiancé, Jason Trawick, at a special event in LA. Jason and Britney teamed up for the City of Hope charity's gala to honor Halston CEO Ben Malka with their Spirit of Life Award at Exchange LA. The evening featured performances from Miley Cyrus and The Pointer Sisters. Britney's been hanging out on the West Coast with Jason and her boys lately — our I'm a Huge Fan winner even met Britney recently, so make sure to check out the whole series! It seems Brit had a great night of letting off steam yesterday. She tweeted a sweet picture of herself and Jason after the bash with the comment, "Had a blast at the City of Hope Charity Gala!"