Keegan-Michael Key on Working on the ‘Only Murders in the Building’ Set (Exclusive)

For Keegan-Michael Key, filming Only Murders in the Building was a career highlight.

Speaking exclusively with PEOPLE at the Play Dirty world premiere in New York City on Sept. 24, the actor, 54, shared that he had a very positive experience on the set of the hit Hulu series.

“It’s one of the warmest, one of the most collaborative, one of the friendliest sets I’ve ever been on in my career,” he says, adding of the cast, “They are wonderful people to work with.”

Key joined the show for its fifth season — which premiered on Sept. 9 — playing N.Y.C. Mayor Beau Tillman.

The Wonka star also shared what it was like watching comedy legends Martin Short and Steve Martin (who play Oliver Putnam and Charles Haden-Savage, respectively) in action on the set.

“Here’s what I learned about Martin and Steve. Martin and Steve are basically not even playing characters. Charles and Oliver, their dynamic is pretty much Steve and Martin’s dynamic in real life,” Key explains.

Key tells PEOPLE he also enjoyed seeing costar Selena Gomez‘s interactions with Short, 75, and Martin, 80.

“One of my favorite things some days on set is to watch Selena [who plays Mabel Mora] just go … It’s so funny to watch them,” he says of the trio. “She’s clearly younger than them by decades, and sometimes she’s the oldest person in the room. It’s quite delightful.”

While Key couldn’t divulge any details about what’s to come as season 5 continues to unfold — “I can’t give clues,” he says — the actor did share that “there is some fun stretching of the artistic muscles that I get to do” in his role as Mayor Tillman.

The latest season of Only Murders in the Building sees Mabel, Oliver and Charles investigating the death of the Arconia’s longtime doorman, Lester, whose body was found in the courtyard fountain at the end of season 4.

In addition to Key, new additions to the show’s star-studded cast include Bobby Cannavale, Renée Zellweger, Logan Lerman, Christoph Waltz, Téa Leoni, Beanie Feldstein, Dianne Wiest and Jermaine Fowler.

Key also stars in the new Prime Video film Play Dirty (out Oct. 1), alongside Mark Wahlberg, LaKeith Stanfield, Rosa Salazar, Chukwudi Iwuji, Nat Wolff, Thomas Jane and Tony Shalhoub. Wahlberg, 54, plays a professional thief who recruits a new team in an attempt to rob a treasure recently recovered from the depths of the ocean. Key portrays art thief Ed Mackey.

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The first five episodes of Only Murders in the Building are streaming now on Hulu. A new episode drops every Tuesday through Oct. 28.