Brad Paisley's new album 'This is Country Music' has quite an A-list guest list. In addition to the already announced duet with Carrie Underwood, Paisley recruited fellow country star Blake Shelton, singer Sheryl Crow, the Eagles' Don Henley and -- drum roll, please -- Clint Eastwood!

According to Country Music is Love, the perennial badass and quintessential cowboy that is Eastwood will appear on an instrumental track that is an "epic movie soundtrack-sounding Western." The unlikely yet head-turning collaboration was born of a friendship that Paisley developed with the actor/director. "I've become friends with Clint and his wife, Dina," the singer says. "So I emailed Dina and said, 'Does he whistle?' And she said, 'Yeah, you want him to whistle on something?' I said, 'I have a thing that sounds like an Ennio Morricone, the guy that did all the spaghetti western music like 'The Good, Bad and The Ugly,' and of course it has to have [makes a whistle sound] all that kind of stuff. I asked, 'Can he do that?' She wrote back and said, 'He'd love to.'"

Eastwood came to the studio and was a consummate pro when recording with Paisley. "We went into the studio and he sang to the track. Sang ... no you don't want to hear that. He whistled to the track, and there he is. It's just little things like that keep me going. The fun of thinking that if you're going to have a Western, have the coolest cowboy of all time whistle on the thing."

Paisley heaped tons of praise on Underwood, saying the former 'American Idol' is "is the best singer in any format of music, I'm convinced. Every take, when you hear the song with her, every take that she did sounded exactly as good as what we choose as far as every time she sang it. I am floored by her and I'm really proud of that moment."

Paisley said that Henley participated with background vocals that sound "like the Eagles a little bit," while Shelton appears on a track called 'Don't Drink the Water.' Paisley said he is looking forward to singing the song with Shelton all summer long as the pair tours together.

The loaded-with-talent 'This is Country Music' is out on May 24.