A celebrity photobomb is a photo to be cherished. It's a very rare, coveted type of photo, kind of like a photo with a dolphin. Not only is getting a photo with a celebrity cool enough on its own, when the celebrity photobombs you it creates a story that goes with the picture. In this case, these two guys got an extremely rare celebrity photobomb: a prince bomb.
That's Prince Harry in the background acting all goofy doing the double thums up. You'd think a prince would be more stuck up, but that's how princes from the old generations acted, not Harry. It is fun to see someone with such a high position and status act as if he's just a normal guy. It makes me think that me, a normal guy, could one day be a prince.