"X-Men: First Class" costars Zoe Kravitz, 22, and Michael Fassbender, 34, couldn't keep their hands off each other during a romantic stroll through New York's West Village on Sunday. Earlier that morning, the two had brunch with a handful of friends, including Kravitz' ex, actor Ben Foster, 30.
Though the costars began dating while filming the Marvel flick in 2010, this is the first time the two have been photographed together (excluding promotional appearances).
So what stopped them from going public sooner?
"They're really low-key, but they have a great time together just talking music or movies," a source tells Us Weekly. "They really didn't want to be a topic of conversation during the press for X-Men."
As for their 12-year age difference, the source tells Us that "Zoe's really mature for her age in that she has very strong opinions and she is very confident in herself. Most people are shocked to learn she's so young; she doesn't really bring it up and age would never stop her from dating anybody."
And, according to the insider, Kravitz (whose parents are Lenny Kravitz and Lisa Bonet) captured Fassbender's heart right from the start.
"For how good-looking and smart he is, Michael's pretty shy," the source tells Us. "She is actually the one taking care of him most the time. She really respects his talent."