BEVERLY HILLS, Calif. (AP) -- Usher was supposed to be one of the performers at music mogul Clive Davis' star-studded bash, but he had to back out for what Davis called a serious illness in his family.

Davis made the announcement moments before Usher was slated to perform in the show. A representative for the singer declined further comment.

But the show did go on in the superstar's absence. With such a plethora of stars in the house, Davis didn't have to go far to look for a replacement in Josh Groban, who took to the piano and sang "Bridge Over Troubled Water."

"This is my first time playing this song," Groban said. Judging from the audience's ovation, it may not be his last.

But Kanye West thought that Groban should have played another tune altogether.

"I think it would have been really cool if he sang 'Love in This Club,'" the rapper joked on stage, referring to Usher's sexy smash hit.

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Taylor Swift boogied as Whitney Houston sang her classic hit, "I'm Every Woman"; Diddy had a photo opp with the Jonas Brothers and Barry Manilow; Katy Perry chatted up the brotherly trio and Rihanna; and good friends Jennifer Hudson and Fantasia partied in the early morning hours with Faith Evans.

There were plenty of A-list moments Saturday night at Davis' pre-Grammy bash, held at the Beverly Hilton. Davis' annual event typically draws a who's-who of entertainment, and Saturday was no different. Prince, Sir Paul McCartney, Sly Stone, Motown founder Berry Gordy, Chris Brown, Diddy and others mingled over the nearly six-hour long event.

Bill Maher provided plenty of off-color laughs during his stint on stage, poking fun at the mother of the octuplets, and the Michael Phelps pot controversy.

"Obviously the message is you can smoke weed and still be at the top of your game," he declared.

There were plenty of interesting sightings. Paul McCartney chatted up director Penny Marshall, while Jamie Foxx and the Black Eyed Peas' Taboo whipped out their cameras when Houston gave her comeback performance. A giddy Hudson, Fantasia and Evans danced and sang along in the audience as Houston was on stage, to Houston's delight: At one point, she looked at Hudson and said, "I'm so proud of you!"

Davis has held his annual pre-Grammy bash for years, but this year, the Recording Academy took over the event and honored Davis as one of their industry icons.