Charlize Theron brought along Sean Penn to watch her pal Seth MacFarlane perform in Los Angeles over the weekend. The Family Guy creator sang for a packed house with Ron Jones' Influence Jazz Orchestra at Vibrato. A source tells E! News that Theron and her boyfriend were "very close the entire evening" as they enjoyed MacFarlane's set. But guests got an unexpected surprise when the blond beauty took the stage to sing alongside her A Million Ways to Die in the West co-star. A candid shot of the two performing their duet onstage was posted on Instagram by Dyler Durden, which shows Theron leaning over in front of the stage.