Robert Downey, Jr. Crashes HBO's 'Perry Mason' Panel at the ATX TV Festival

The Perry Mason panel at the ATX Television Festival had a last-minute surprise guest. As the hour-long conversation, which was webcast to YouTube Friday night, was starting to wind down, Robert Downey Jr. star popped up alongside his wife, Susan Downey, who executive produces HBO's upcoming take on the iconic character.

When the moderator, TV Guide's Jim Halterman, asked the assorted cast and crew when viewers would be able to watch the legal drama's latest iteration, Downey Jr. popped up in the corner of his wife's screen, proclaiming "I'll take this one, Jim." As the rest of the participants reacted to the actor's sudden appearance, he quipped that he'd "been on my heels for 92 minutes" while the panel took place.

"First, I'd like to say the usual: you're welcome," Downey joked again, before mentioning that he'd spent some time himself developing Perry Mason, which he promised couldn't have "ended up in more capable hands," adding "for that, I'm very grateful." After announcing the show's June 21 premiere, he continued "That's the slot, by the way. That 9 p.m. Sunday slot, that's the good one." Before the panel formally wrapped, he went on to observe that "sitting here this whole time, this long format, I actually understand what the show's about now, so thank you."

Kicking off the panel, Susan Downey explained that she'd been developing the series roughly for or five years ago. After mining the massive backlog of Perry Mason material, created by author Erle Stanley Gardner, she said that she wanted to "not have the Perry everybody knows." Her sentiments were echoed by The Americans star Matthew Rhys, who plays pop culture's most revered lawyer.

"They pitched this very dark Mason, that came with a lot of baggage," Rhys explained. "[He's] very much an outsider, which I found very interesting. So much of the backstory is presented and is given, from his time as a WWI veteran, his family problems, his inherited land problems, the new Los Angeles emerging, he's got a lot on his shoulders."

Perry Mason stars Rhys alongside John Lithgow, Tatiana Maslany and Shea Whigham. As the Iron Man star promised, the series will premiere Sunday, June 21, and will be available to stream on HBO Go, HBO Now, and HBO Max.