Singer Aaron Carter sings to a crowd during a First Night celebration at Government Center,in this Dec. 31, 2004 file photo in Boston. (AP photo)

LOS ANGELES - Aaron Carter has broken off his engagement to his older brother's ex-girlfriend, his representative, Juliette Harris, confirmed to The Associated Press.

The 18-year-old pop singer called off his engagement to 22-year-old actress Kari Ann Peniche just a week after he proposed onstage in Las Vegas, Harris said Monday.

Peniche is an ex-girlfriend of Carter's 26-year-old brother, Backstreet Boys singer Nick Carter. She's also a former Miss Teen USA and former Playboy Playmate.

"I got caught up in the moment and proposed," the younger Carter told Us Weekly magazine in a report on its Web site. "I then realized it was a hasty thing to do and I am not ready for marriage quite yet."

Both brothers will appear in the reality series "House of Carters," which debuts Oct. 2 on the E! network.