You never know who's going to pop up at a Garth Brooks concert! On Thursday night (Dec. 4), the country legend performed in St. Louis, where a superstar showed up to fanboy over the guy he calls one of his "idols."

Justin Timberlake took a night off for a little R&R -- country style. The pop icon attended Brooks' concert at the Scottrade Center, and it seems he had one heck of a time. Timberlake even got some one-on-one time with Brooks after the show, sharing the special moment with his Instagram followers.

Although Timberlake didn't sport his country duds, he sure does look happy! He wore a black jacket and black hat and stood pretty close to Brooks, who was a little more dressed down in his Eskimo Joe's sweatshirt. Timberlake's smile may have said it all, but he elaborated in an excited caption, writing: "One of my IDOLS. Garth... You are a MASTER of your craft. I am in awe of you, still."

Kim Kardashian was put in her place when Timberlake's excitement over attending the concert nearly broke the internet -- or at least Twitter. Fans were tweeting up a storm about Timberlake's presence at the event and at seeing two massive stars coming together.

And despite his megastar status, the 'N Sync hitmaker didn't watch Brooks from backstage ... but from the front row! A fan captured a hilarious image of the singer having the time of his life, dancing and singing along to Brooks' top tunes.

Perhaps someday Timberlake will consider bringing country back? Click the button below to see what we mean.