Inside Madonna's 50th Birthday Bash

By Monique Jessen and Caris Davis

08/18/2008 at 10:45 AM EDT

Fifty has never looked so fabulous!

Madonna celebrated her 50th birthday Saturday at a trendy London club Volstead.

"It was a small party," a source confirms to PEOPLE. "A private event for her close family and friends. It was low key."

And despite lingering rumors of marital strife, the elaborate bash was organized by her husband Guy Ritchie.

"She looks better now than she ever has done," her director husband told the 90 gathered guests, according to Britain's The Sun. "I'm so proud. I love her so much."

Highlights of the evening, which had people dancing til 3 a.m., included Madonna's daughter Lourdes serenading her on the piano and illusionist David Blaine performing card tricks.

Later, as the deejay blasted the singer's greatest hits, she hit the dancefloor with Lourdes and sons Rocco and David.

But it was back to business Sunday morning, when the pop star was spotted heading to the gym for her usual daily workout.

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