"Our friendship really started when we did the Zaxby's commercial and we were at Tyler Hubbard's wedding," says Rhett. "We kind of realized that we had a lot of the same friends. And my wife loves him, and you can't deny that Brett is just the most ultimate dude in the world."
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Plus, friendship is heavily influenced by people sharing a common world view. And not many share the world view of an artist -- especially that of a singer making soul music for country fans with their second album in 2015.
"We're both in a really cool spot where our careers have kind of risen together," notes Eldredge.
Eldredge got a bit of a head start. His debut single, "Raymond," was released to radio five years ago -- on Aug. 30, 2010 -- but it wasn't until his third release, 2012's "Don't Ya," that his career kicked into gear. That single and the two that followed it, "Beat of the Music" and "Mean to Me," rose to No. 1.
Meanwhile, Rhett made his first appearance in 2012 with "Something to Do With My Hands" and similarly hit his stride on the third release, with "It Goes Like This," "Get Me Some of That" and "Make Me Wanna" each reaching the Country Airplay pinnacle in succession.
In the process, both of them found their grooves, and they ended up being similar textures. Eldredge, whose love for Frank Sinatra had him marketed initially as a crooner, locked onto more of a blue-eyed soul identity. His versatility actually made that process something of a challenge.
"I grew up listening to so many different kinds of music from Sinatra to Brooks & Dunn to Vince Gill to Ray Charles," says Eldredge. "And I loved Ray Charles. When I hear Ray Charles' voice, I literally get chills."
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By contrast, Rhett's rhythmic leanings were evident from the start. Part of his history includes doing hip-hop songs at the occasional concert by his father, singer-songwriter Rhett Akins, as a pre-teen, and Rhett's debut album had a handful of songs that played with rap and disco. His 2014 single "Make Me Wanna," inspired by the Bee Gees' "Stayin' Alive," increased his confidence in a country/R&B hybrid, and his new album -- Tangled Up, due Sept. 25 -- ventures into Motown, funk and hip-hop, testing boundaries that previously seemed unreachable for a country song.
"We went all the way to the line [of acceptability], and we might have crossed it slightly," says Rhett of Tangled Up. "I think the moment we might have crossed it slightly was when we were like, 'OK, I think we're done, and I think we need to stop at these 13 tracks and put them out.' I'm that kind of guy, and I've always been that kind of guy, that really loves going farther than I probably should."
One of the biggest differences between the two is their regional background. Rhett hails from Georgia, a state that has bred a long line of recent country hitmakers, including Jason Aldean, Brantley Gilbert, Luke Bryan and one-half of Florida Georgia Line, just for starters.
Eldredge grew up in the Midwest -- Paris, Ill., to be exact. Fewer country stars have graduated from there -- Illinois' lineage includes Gretchen Wilson, Alison Krauss, David Lee Murphy and Suzy Bogguss -- though the region is a natural piece of the genre's audience.
"Iowa's one of the countriest states ever," says Rhett Akins of Illinois' neighbor.
It's one of the reasons that Eldredge named his new album -- Illinois, issued Sept. 11 -- after his home state. He also wrote the title track with Tom Douglas ("The House That Built Me," "Raise 'Em Up"), weaving in the cornfields, snow drifts and Little League baseball that inform his cultural history.
"No matter how far you go in life, that place that you come from is what makes you who you are," says Eldredge. "And Illinois made me who I am."
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The Georgia/Illinois pairing of Rhett and Eldredge on the Suits and Boots Tour seems like a natural. They're close enough in career stature that they plan to flip a coin to establish the closing act on the first night and trade off the role after that, though they'll do a tandem set as a finale each evening that makes it a pure co-headlining arrangement.
They're in artistically similar places, bringing an R&B flavor to contemporary country, and in a visually similar spot, too, often wearing suits onstage. Which is one reason they chose the Suits and Boots moniker for the tour, though, if they wanted to rhyme, Brett and Rhett was available, too.
"My idea was calling it 'Thomas Brett,'" says Rhett, "but we wanted to have like a legit title, and I think [Suits and Boots] kind of fits."
The R&B material emphasizes the playful part of their nature. But the fashion component is meant to offset that with a little more weight.
"People like Bradley Cooper in the movies -- I take 'em even more seriously," says Eldredge, "when they throw a suit on."
This article first appeared in Billboard's Country Update -- sign up here.