Back when he was Mr. Spears, there were a lot of negative things said about Kevin Federline, but chubby wasn't one of them -- the former dancer-turned-babydaddy was nothing if not slender. But things have changed since he and Brit broke it off -- he seems to have gone from chump to chunk at an alarming speed.

Check out these photos of K-Fed out and about with his new woman. He's noticeably ... um ... heftier, shall we say? In fact, he appears to be borderline obese. That's not a very good example to set for the kids, K-Fed. And anyway, what happened to the workout DVD that was in the works?

However, his other ex, Shar Jackson, is quick to jump to his defense. "It's daddy weight!" she says. "When you are a full time parent, sometimes you can't focus on you. If gaining a few pounds is your only problem, life's not too bad!" Adds his spokesperson: "'He's very happy with the way he looks."

I hate to say it, but maybe he should check out Britney's workout video? Just a thought.