Jessica Simpson and John Mayer Split

Mayer and Simpson very recently split up, and sources told PerezHilton.com that is was Mayer who broke up with Simpson.

"They officially called it quits this past weekend," a source told the site. "They'd been having problems for a while now and just decided it'd be better to end things."

Just a few days ago, Simpson's father was praising Mayer in the press.

While Jessica is currently at the Cannes Film Festival — smiling for the cameras — John also appears to be delving back into the single life, according to Perez.

Mayer and pals partied at New York City club Stereo on Thursday night, and the rocker was having a really good time.

"He was way tipsy and was spending a lot of time with an ugly brunette that was not Jessica Simpson," a source told PerezHilton.com.

Why did they break up? As reported in Pop Tarts Thursday, Simpson was said to be furious that Mayer lingered and laughed with the pretty Roberta Armani (Giorgio's niece) at last week's Costume Institute Gala, according to Australian magazine Famous.