Garth Brooks has accomplished something that no other artist in history ever has -- he's earned seven diamond album certifications -- and to celebrate the monumental achievement, he hosted a free acoustic concert at Nashville's Ascend Amphitheater on Monday night (Oct. 24). But it wasn't just the country superstar himself who appeared onstage during the show; rather, several other artists joined in on the fun.

"This state has treated me like I was a native son," Brooks shared after an introduction from Tennessee Gov. Bill Haslam, before welcoming to the stage a fellow native of his home state of Oklahoma, Reba McEntire. Together, the two performed "Not Counting You," a song from Brooks' eponymous debut album.

"I can't tell you how much of an honor it was to grow up knowing that anything was possible if you were from Oklahoma because this woman was doing it all," Brooks gushed of McEntire. She, meanwhile, recalled the pair's first show together, in Illinois, when Brooks was her opening act: "My tour manager came up and said, 'You're not going to believe this guy who's opening for you tonight ... He's all over the place.'"

Following McEntire's appearance, Chris Young joined Brooks to sing "The River," from Brooks' Ropin' the Wind record. From stage, Young admitted, "I actually had posters of you on my wall when I was a kid ... This is one of my favorite songs of all time."

With the crowd on their feet, Brooks launched into an introduction of his next guest, Jason Aldean: "Everybody that is before you is a god ... And the guys that come after you, you always look at as if they're younger, and they've got things that are different from you. Very rarely do you fall in love and look at these guys as one of your heroes ...

"The muscle [Aldean] brought into country music opened the door for guys like me even to record songs with a little more muscle to them," Brooks added, with Aldean noting that Brooks was "the guy that broke down a lot of doors for me and allowed me to have a career in this business."

Aldean and Brooks sang "Much Too Young (to Feel This Damn Old)," from Brooks' freshman disc, before Brooks brought "my best friend" Trisha Yearwood to perform their first-ever duet, "In Another's Eyes," which appears on Brooks' Sevens album.

"As your wife, I would, of course, be nowhere else but here. But as a fan and as someone who has known you since before your first single came out, I just want everybody to know that the guy that I met in 1987 is the same guy -- same really nice, kind, compassionate, good guy," a beaming Yearwood shared with the crowd. "You taught me how to be a boss. You taught me to be a friend to people. You taught me how to treat the people around me, reinforce what my parents had taught me. As your wife, I'll tell you all the things I love about you when we go home. But as a fellow artist, I'm just proud of the person that you are, and I'm honored to be a part of your life."

After "In Another's Eyes," Brooks ceded the stage to Yearwood, who performed her own hit, "Walkway Joe." Brooks then invited Steve Wariner to the stage, and the two performed "Longneck Bottle," also from Sevens, trading guitar licks and vocals throughout.

"When you talk about reasons why you're in this business, [Wariner] is one of the reasons why I'm here," Brooks noted. "Fantastic entertainer, fantastic songwriter. I never had any dream that he would be a great friend."

Special guest Kelly Clarkson sang "We Shall Be Free" from Brooks' The Chase before Brooks, at Clarkson's suggestion, invited Wariner back to the stage to sing his hit "The Weekend." Brooks performed the rest of his show solo, with his set including at least portions of several of his biggest hits: "Two Pina Coladas," "Unanswered Prayers," "If Tomorrow Never Comes," "Papa Loved Mama," "Callin' Baton Rouge" and "The Dance."

"How fitting is that?" Brooks asked the crowd when it was just him up onstage. "Because it's you and God that's given me everything I've got."

A representative from RIAA was on hand to present Brooks with his seventh diamond trophy, and Jack Daniel's gave Brooks his own personalized barrel of whiskey. The evening concluded with Young, Yearwood, Wariner and Clarkson reuniting with Brooks onstage to sing "Friends in Low Places" before a colorful fireworks display lit up the sky.

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