The setting was Friday's CAA party at the Buffalo Club in L.A., where DiCaprio and his girlfriend Bar Rafaeli came face to face with Bundchen and her husband (and father to her new son) Tom Brady.
DiCaprio, 35, and model Rafaeli, 24, were the first to arrive, where they sat in a booth with pal Kevin Connolly and munched on "a plate of buffalo wings," the observer tells Us. The pair were "really at ease" and "openly affectionate," with Rafaeli sitting in DiCaprio's lap for several minutes.
Later in the evening, Bundchen, 29, and Brady, 32, walked by the other couple's table. "Leo actually kissed Gisele on the cheek and said hi," the eyewitness says. "Brady and Bar just sort of looked on at their partners and each other. It was an awkward moment but it was over instantly. Brady and Gisele had more important things to do."
At one point during the party, the supermodel and football star shared a kiss a few feet away from DiCaprio. "Gisele and Brady seemed totally in love," the eyewitness says.
DiCaprio and Bundchen dated from 2001 to 2005. The actor and Rafaeli recently reunited after an extended break in 2009. Bundchen and Brady wed in February 2009, and welcomed their son, Benjamin, in early December. "I am living a very special moment in my life," Bundchen wrote soon after Benjamin's birth.
The glitzy Golden Globes weekend set the stage for other nervous-making encounters between stars and their exes -- including Julia Roberts and Kiefer Sutherland, plus Katie Holmes and Chris Klein. Read more in the upcoming new issue of Us Weekly, on newsstands Wednesday!