Chicago, Illinois - Olivia Rodrigo and Yungblud jumped onstage with Smashing Pumpkins for their packed Lollapalooza set. The crowd probably couldn't believe their good luck!

Billy Corgan shocked the mob of Chicago festivalgoers by bringing Yungblud back to sing Luna soon after his own set.

"This is a f***ing dream come true," the latter gushed, per Rolling Stone.

The big standout, however, was a cameo from pop-rock superstar Olivia Rodrigo!

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After Yungblud left the stage, Corgan announced that he's likely "to bring out a very, very special guest ... Miss Olivia Rodrigo!"

Understandably, the crowds went bonkers for the singer, whose June record, You Seem Pretty Sad for a Girl So in Love, is still doing massive numbers on the charts.

Sporting a white fluttery babydoll dress and white knee-high stockings with heels, Liv performed an acoustic rendition of the Smashing Pumpkins' 1995 hit, Thirty-Three.

The night was lit by red light while rain fell around them for what is now a truly iconic Lollapalooza moment to remember.

Smashing Pumpkins featured another unforgettable guest star earlier in the week when they brought actor Barry Williams — aka Greg Brady from the 1970s sitcom The Brady Bunch — to sing the fictional family's famous song, It's a Sunshine Day.