Not long after having a glamorous hang out session with Beyoncé [1], Mariah Carey [2] had a very special, very unexpected guest at her Las Vegas show on Friday night: Will Ferrell [3]. The pop diva, who's performing her show "Mariah #1 to Infinity" at Caesar's Palace, looked like she was thrilled to be meeting the actor. She happily posed for photos with Will, writing [4], "Shake and bake!! Thank you for coming to my show last night!! #elf forever!!" The newly engaged singer [5] also gave the Zoolander 2 actor a small touch-up with her makeup and got in a group shot with a few members of her crew and Will's wife, Viveca Paulin. Keep scrolling to see the pair's hilariously random interaction, and then check out Mariah's most adorable mom moments [6]!