Party animal Michael Phelps surprised people by being "really nice" at Jay-Z's concert in Atlantic City last weekend.

"He stayed very under the radar throughout the concert and even later at the club," the New York Daily News quoted a guest, as saying.

The source added: "He kept a hat on and was only drinking casually. He was really nice to girls that wanted to take pictures with him, but would excuse himself right after. He looked like he didn't want any attention."

According to an informer, Phelps is trying hard to mend his ways after snaps of his wild partying landed him in trouble with his sponsors, coaches and his fans.

"He's really trying to put that behind him," the insider said. (ANI)