It works to have friends in Hollywood, and Charlie Day and Guillermo del Toro have become very good friends. In fact, they've become such good friends that del Toro is going to guest star in the upcoming season of It's Always Sunny in Philadelphia.

Stars and executive producers/writers Glenn Howerton and Rob McElhenney announced the news this morning during a conference call with journalists. Apparently while Day was filming del Toro's Pacific Rim, he learned the director is a big fan of the FX comedy. At that point, they decided to write him into a role.

"He really wanted to guest star, so we wrote him in this year, too, and it's really fun," Howerton said.

In addition, P. Diddy will make an appearance during Season 8. Even after seeing him go off the rails in Get Him to the Greek, Howerton promised this is going to be a new type of role for the rapper.

"We've got a really fun guest star role for Sean Combs," he said. "I'm excited for people to see it, because it's very, very different from anything at least I've ever seen him do on anything."

McElhenney and Howerton also talked about when the end of It's Always Sunny will come. Although the duo teased that the show doesn't have an end date when we caught up with them on the Sunny premiere red carpet, McElhenney admitted today it probably won't go past 10 seasons.

"I think our goal for the show is always to surprise people, because we think that's the best way to achieve comedy," he said.

Howerton jokingly disagreed, saying that he doesn't want the show to end until they've broken Bonanza's or The Simpsons's records.

It's Always Sunny in Philadelphia premieres tonight at 10 ET/PT on FX.