In the brand-new episode, Sean joins the show as Kip Withers, Carol Miller's (Margo Martindale) new best friend and a new archenemy for her son Nathan (Will Arnett).
Will filled us in on how Sean's casting came about, telling ET's Kevin Frazier that he may have had a hand in the decision.
"Sean and I have been friends for a long time," said Will. "We were actually on vacation together in Istanbul, Turkey and two weeks later Greg Garcia, who created our show, called me and said, 'Hey, I'm thinking about writing this new character. What do you think about Sean Hayes?' ... I said, 'Yeah, of course! Sean is hilarious. He's one of the funniest people I've ever known."
Sean's role was something of a homecoming for the actor as he shot Will & Grace on the same lot that The Millers currently films on. Interestingly, Will was also featured on Will & Grace in 2004 where their characters had a dance off while auditioning as backup dancers for Janet Jackson.
"We met before that, but that's where we first became friends," said Will.
The Millers airs Monday nights at 8:30/7:30c on CBS.