Zuck, as he's called by friends, gave an impromptu 23-minute tour of his old haunt Tuesday on Facebook Live, holding his phone as he walked around the building telling stories about Hot Pockets snacks, small beds and bad roommates.
"I think there is probably some good karma here," he said.
At one point he remarked about how more than 100,000 people were watching and by the time it finished, nearly 2 million people had watched.
Among the stories he told were of Facemash, a prank of sorts that asked students to rank one another's looks. When Zuckerberg realized it had taken off, he claimed he tried to shut it down, but couldn't log in to his laptop. So Harvard threatened to shut down internet access across his dorm instead.
"That was pretty real, back then," he said.
Priscilla Chan, Zuckerberg's then-girlfriend who's now pregnant with the couple's second child, joined him on the tour and told stories about their opposite sleeping schedules and how much of a night owl Zuck was. She'd typically wake up around 5 a.m. just around the time when he'd go to sleep.
"When you're programming you want it to be quiet," he said.
Zuckerberg will be giving Harvard's commencement address on May 25, during which he'll finally receive a degree more than a decade after dropping out to work on Facebook