In his first Q&A via Facebook Live posted to his personal page, Zuckerberg revealed he has a broken arm.
"People don't believe me because I don't have a splint or a sling," he said during the stream on Tuesday. "Apparently when you're trying to heal an elbow or a shoulder, if it's not too badly separated, the mobility actually helps it heal, more than just having it in a sling that makes it a little stiff."
But Zuckerberg wasn't alone during the Q&A and was joined by comedian Jerry Seinfeld. The CEO even took some time to explain how he got the injury, revealing to Seinfeld that it came after taking his New Year's resolution to run 365 miles in 2016 a little too extreme.
"That is not a challenge," Seinfeld said in response. "A mile a day."
"I have a way of making things more intense than they should be ... It's gone too far," Zuckerberg admitted. "I've how gotten to the point where I can basically wake up in the morning and bang out a half marathon or a marathon if I want."
When it became too easy to just run, Zuckerberg decided to train for a triathlon. However, "ten seconds" into training on his bicycle last week, Zuckerberg explained he fell off and fractured his radius bone.
The Facebook Live post, which has since racked up over 8 million views and 515,000 likes, comes as the tech giant is focusing on the platform, as Fortune wrote about. Zuckerberg is calling the platform the way of the future.