Titled HBO Backstories, the new web series of behind-the-scenes stories kicks off with co-creator David Benioff recalling Momoa's cameo in a dreamy hallucination scene for the Season 2 finale. After filming, everybody went out for a drink, and Benioff decided to challenge Momoa to the slap game. I was like I'm going to challenge the Khal because if I beat the Khal, I'm the Khal," said Benioff. That's how he ended up in the hospital. ALSO: Momoa shaves off his famous beard for the first time in seven years to discourage plastic bottle use.