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5 Seconds of Summer (5SOS) surprised some lucky fans on Saturday by personally selling them tickets to their upcoming show.

The Australian boy band is slated to play its first U.S. headlining concert this fall at The Forum in Inglewood, Calif., and fans were camped out overnight to score tickets.

They were then shocked to discover Luke Hemmings and the guys actually manning the venue’s box office.

The group went on to treat fans to a special outdoor, acoustic performance of their hits “She Looks So Perfect” and “Amnesia,” and further surprised by bringing out a mariachi band and assorted goodies, in addition to holding an autograph signing.

“We wanted yesterday to be epic for you guys… So we did this lol, cause what’s more epic than this,” 5SOS wrote on Facebook Sunday morning.

They continued, “For us this has been one of the biggest weeks of our lives. Thankyou to anyone who has the album… You guys mean so much to us. We’d still be practicing inAshton’s garage if it wasn’t for you. Thankyou thankyou thankyou !! X

Their self-titled debut album was released in the States last Tuesday, and is expected to be number one on the Billboard chart.

Check out more from the event below!

Photo: Getty Images