OHMYGOSSIP — Perry feels like a fool. The singer is apparently doubting that Russell Brand — who she recently split from after a short marriage — was the “changed man” he claimed to be when they married in October 2010.

“I’m such a fool,” Katy recently confessed to the pal. “I believed in him.”

According to America’s Life & Style magazine, Russell has been clubbing and coming on to women all over LA.

“It’s very disturbing to Katy that he’s moved on so quickly,” a source said.

“She was shocked to hear that he was out partying again and trying to pick up girls. It sickens her — she feels humiliated and burned.”