Happy Birthday, Mr. President!

Like Madonna and many other stars, Lady Gaga channeled glamour goddess Marilyn Monroe in Hollywood over the weekend. But Gaga's retro getup was for the benefit of none other than former President Bill Clinton, the guest of honor at Saturday's Decade of Difference concert at the Hollywood Bowl, which marked both his 65th birthday and the 10-year anniversary of the Clinton Foundation.

To meet the former Commander-in-Chief backstage, the "You and I" singer, 25 (real name: Stefanie Germanotta) wore her blonde hair in a bouffant, a classic gold gown, elbow-length gloves and a faux beauty mark -- all in a nod to Monroe, who died at age 36 in 1962 (and who famously was linked romantically to President John F. Kennedy).

"A highlight of tonight was meeting Lady Gaga backstage," Chelsea Clinton raved on Facebook. “Her combination of creativity, intelligence and activism are inspiring -- and, yes, she’s even more remarkable on stage than on youtube."

Onstage, Gaga stripped down to a nude bodysuit and serenaded the President with "Bill Romance," changing the lyrics to her smash "Bad Romance."

"I'm going to dance with the whole family." She sang, "I love you Bill, and Chelsea too."

Admitted Clinton before the big night: "I got nervous when Gaga said she was planning to have a Marilyn moment, and I thought, 'I will have a heart attack for my 65th birthday.'"