A friend posted a nude Picture of his gf in his story

Hey yall, imma need some advice. Today i got a notification from snapchat that a friend of mine posted a story. I clicked on it and was not ready for what i was about to see. Just a topless picture of his (16yo) gf. He took it down after 2-3 minutes but the damage has happened. He just posted a nude picture of his underage gf in his story. I mean accidentally posting a picture as a story on snapchat instead of sending it to a friend has happened to the best of us. But if he wanted to send it to a friend it just makes the whole thing worse. I dont even think that she has snapchat so she probably doesn‘t even know. And i think there is no way that he is gonna tell her. Im a little bit clueless here, because i dont even know her. What should i do here?