Ex-boyfriend John Mayer might be in the doghouse, but that doesn't mean Jessica Simpson cannot say something nice about the ex who broke up with her on her 29th birthday.

The singer had nothing but praise for Dallas Cowboys quarterback Tony Romo -- and his famous posterior -- during an appearance on 'The Late Show with David Letterman' airing Wednesday, according to People.com

"Tony is great, still a friend of mine," Simpson said, admitting she checks out the action when Romo is playing. "I still look at his cute butt in the outfit -- uniform."

Asked by Letterman what caused them to split, she said, "What went wrong? You'd have to ask him that. He broke up with me on my birthday."