Only ET's Mary Hart is on the set of "How I Met Your Mother" when series star Neil Patrick Harris tests his acting chops against TV legend Regis Philbin, who takes a break from his hosting chores on the New York-based "Live with Regis and Kelly" to head to Hollywood.
Regis landed the gig after Neil, who is nominated for an Emmy Award this year, appeared on Regis' "Million Dollar Password."
"The [contestant] lost everything," Regis recalls. "He collapsed. He wasn't kidding. Fell to his knees and Neil Patrick Harris walked away. That's tough buddy."
In this upcoming episode, Regis plays himself -- but as a tough guy.
"I'm punching people out. It's really funny," Regis tells Mary, who recalls that the talk show host formerly took a truckload of vitamins.
"Every meal," he says. "I took 75 vitamins."
"How I Met Your Mother" returns with new episodes on Monday, Sept. 22 at 8: 30 p.m. on CBS.