Caitriona Balfe and Sam Heughan's characters have an epic romance on Outlander, but off screen, the two have an epic friendship. Case in point: Caitriona's recent birthday messages to Sam. In honor of the Scottish actor's 38th birthday, Caitriona decided to completely troll her costar by posting a number of hilarious photos on Instagram. "Happy Birthday darling!!!" she wrote alongside a photo of Sam photoshopped on her body. "May you feel like a princess alllllll day 😘😘 @SamHeughan 👸🏻👸🏻👸🏼👸🏼." And that's just the icing on the cake . . . pun intended. See the hilarious messages ahead, and then see which other lucky celebrities are part of Sam's inner circle.