The U.S. pop star and British comedian Russell Brand were married for about 14 months before Brand filed for divorce Friday.
The Post said the breakup didn't seem to keep Perry from being in what appeared to be a festive mood New Year's Eve.
"Katy was in a private room with a group and she seemed to be in a great mood. She spent most of the night dancing and laughing with friends," a witness told the newspaper. "One wouldn't have ever even known that her husband had just filed for divorce. At one point, she was talking to a guy with long hair down to his shoulders in the hallway. They were talking for a while. She was smiling and leaning up against wall. ... She looked like she was having a great time."
Brand spent New Year's Eve at the Savoy Hotel in London with friends, including singer Florence Welch.
"I'm doing good. Everything is going to be better next year," the Post quoted him as saying.
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