The tradition of famous ladies wishing the president a happy birthday in song dates back to Marilyn Monroe's sexy rendition for John F. Kennedy in 1962. This year, it was Jennifer Hudson who serenaded Barack Obama on his 50th birthday celebration in Chicago, but unlike Marilyn, she didn't act alone.

Hudson, 29, was joined onstage by Chicago mayor and Obama's former White House Chief of Staff Rahm Emanuel, jazz pianist Herbie Hancock and members of the band OK Go. Hudson, who is a Chicago native, also held her microphone to the 2,400-member audience, which joined in on the song.

Though she shied away from the sparkling Hollywood glamor of Monroe, the former American Idol contestant looked fantastic in a slim black dress with a heart-shaped top. Now a spokesperson for Weight Watchers, Hudson has dropped at least ten dress sizes since her Oscar-winning turn as Effie in Dreamgirls.

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