Lady Gaga and Stevie Wonder united at Elton John's birthday party to sing Wonder's 1981 hit "Happy Birthday." The event raised money for both the Hammer Museum and the Elton John AIDS Foundation.
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Gaga returned to her natural hair color, brunette, in a classic updo for the event, and wore a gorgeous Alberta Ferretti gown. In addition to dueting with Wonder, she found time to sing piano renditions of "Bad Romance" and "Born This Way."
Take a look at Gaga and Wonder, as well as some classic Fame Monster piano-ballad Mother Monster, below.