Thanks to their high-profile gigs as The Voice judges, Blake Shelton and Maroon 5 frontman Adam Levine's bromance is well-documented — but we haven't forgotten about Shelton's original bromance. That's right: Years before Levine, there was Trace Adkins.

Shelton and Adkins have known each other for years — there's a photo in the gallery below from all the way back in 2004! — and have shared the stage together many times over the years, most recently during Shelton's 2019 Friends and Heroes Tour. Their most famous collaboration, however, came in 2009, when the pair released the song "Hillbilly Bone." The No. 1, platinum-certified hit earned the pair an ACM award for Vocal Event of the Year.

Adkins was the one who invited Shelton to join the Grand Ole Opry in 2010. In 2018, Shelton invited Adkins to serve as his The Voice team's advisor during the show's 14th season. And on Friday (Aug. 16), the pair will release a new collaboration together, "Hell Right."

"The guy's got so much personality in his voice and the way he sings," Shelton says of Adkins, "and I still think he's one of the most underrated vocalists out there."

Flip through the photos below to see the Shelton / Adkins bromance evolve over time.

Blake Shelton + Trace Adkins: The Original Bromance