The cast of Star Trek: The Next Generation were surprised when a fan's photo opportunity turned into a surprise proposal. Wil Wheaton tells the story:
About 30 minutes or so into this particular session, these two people came in. The girl went to stand between Patrick and Frakes, and the guy directed her to stand in the front, instead. All of us tried to figure out what was going on (usually it's small kids who come to the front, usually sitting on Brent's lap or Gates' lap), and the guy said, "I really love Star Trek, but I love [her name] even more." He got down on one knee, and proposed to her.
Marina started to cry, I felt like I was going to cry, and we all applauded and celebrated when she said "yes." Apparently, they'd met Marina earlier in the day, and Marina had given him shit for not marrying her, so Marina was embarrassed about that.
The photograph snapped at that moment managed to capture the famous Picard facepalm. Link