But once they met on the set of their movie, they began quietly dating in 2009.
Not only did they attempt to keep things under wraps because Natalie's a private person, but there was also the whole pesky issue of his former live-in girlfriend...
Dec. 31, 2009: Portman and Millepied are spotted at a New Year's Eve party in TriBeCa, according to Page Six. This is also right around the time that his former girlfriend of three years moves out.
"She was a ballerina at the American Ballet Theater," Page Six reported, "She had been talking about marrying him and was blindsided by the split. She moved out right after New Year's Eve."
January 2010: The dancing duo are photographed during an outing to see the Gyor National Ballet perform in NYC.
August 2010: The low-key twosome are clearly getting more serious, and photographed doing couple-esque things, like having lunch dates in LA and taking Natalie's dog to the vet.
September 2010: The couple hit the Venice Film Festival to promote Black Swan. Although they're photographed sitting together, there's no PDA or handholding in the press pics.
November 2010: They continue to play it cool at the Hollywood premiere of their film, walking the carpet solo and only taking photos with the entire cast.
Dec. 3, 2010: Their movie, Black Swan, opens in limited release to critical acclaim and box office success. Millepied was originally only supposed to choreograph behind the camera, but ended up asking to play the Swan Prince opposite his real-life leading lady. Portman doesn't confirm their couple status, but praises his "creativity, intelligence and flexibilty" during an interview.
Dec. 27, 2010: Natalie drops a baby bombshell! Her rep confirms to E! News that she and Benjamin are engaged and expecting a child in 2011.