"It felt like it was something you could put on and just be chill," brother TJ says

By Sarah Michaud
Updated March 04, 2016 02:15 PM

When it came time to follow up “Stay a Little Longer,” the rockin’ No. 1 hit that earned them a Grammy nomination, Brothers Osborne looked back, not forward, for inspiration.

Their new single “21 Summer” “happens to be one of the earliest songs we’d written as Brothers Osborne,” older brother John tells PEOPLE exclusively. “We knew if it lasted this long there must be something special.”

He adds, “We wanted to show another side … ‘Stay a Little Longer’ was a big epic production so we wanted to give the listener something they haven’t heard yet.”

“It felt like it was something you could put on and just be chill. You could sit on your back porch and just hang out and have a conversation. We loved that idea,” younger brother TJ explains in the above video. “We were like, ‘Man, we have those songs that are a little bit more in your face but it would be cool to have a song that was just very relaxed.'”

Their long-awaited album, Pawn Shop, also featuring 2014 hit “Rum,” was released in January – “the response has been amazing and we couldn’t be more grateful,” John says – followed by a trip to the Grammys for their best country duo/group performance nomination in February.

“Being at the awards was a dream come true, but the afterparties are pretty insane. Justin Bieber was attending one that we went to, so just getting through the mob of paparazzi was intense, but once we got inside it was packed with the most successful and respected people in the entertainment industry,” TJ tells PEOPLE.

“I got to talk to Gary Clark Jr. about his performance that afternoon, and I was blown away by how nice and humble he was. A true legend, that guy.”

With “21 Summer” most added at country radio this week, the brothers celebrated their success with a No. 1 party for their previous single Wednesday in Nashville. Next up for the pair? Heading to Las Vegas for their two ACM Awards nominations on April 3 before hitting the road with Miranda Lambert and Kip Moore this summer.

“It’s going to be a blast. John and I have seen both of them play and they bring it, so I can promise you that every show we play we’re going to give it all we got,” TJ says.

“This will be the first tour where we’ll get to try some of our new material from the album, so we’re excited to see what the fans are responding to the most. In other words, GET READY TO PARTY!”