Billie Joe Armstrong has been throwing it back a lot recently. At the start of the month, the Green Day vocalist threw it back to 1981 and performed Kid Wilde's "Kids In America" for his "No Fun Mondays" cover series. Now, Armstrong is revealing some behind-the-scenes secrets about their 1994 album Dookie after a Sesame Street fan edit surfaced online.

On Sunday, Armstrong took to Instagram to share the reason why the original back cover art for Dookie had to be changed. He also revealed that after 26 years since the album's release, he still wonders what happened to one of the girls featured in the back cover art.

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Dookie is one of Green Day's most iconic albums. Featuring the hits "Basket Case" and "When I Come Around," the album's contents have stood the test of time since its release over two decades ago. However, some fans may be unaware of the problems the band ran into regarding the album's original back cover art.

This week, Armstrong shared a fan edit of Dookie's back cover art that featured Armstrong's Sesame Street character. The fan edit is in reference to Dookie's original back cover that some may not know about.

Dookie's original back cover art featured a plush-toy of Ernie from Sesame Street. However, the image was later removed from the cover due to fear that the children's show would file a lawsuit. As well, the band worried that some may identify Dookie as a children's album.

As Armstrong shared in his Instagram post, a grandmother did actually purchase Dookie for her grandchildren after seeing Ernie on the back cover. This event is what initially sparked the decision to remove the Sesame Street character from the artwork.

"The story goes a grandmother bought Dookie for her grandchildren because she thought it was a children's album," Armstrong says. "Whoops. And well...we had to take Ernie off."

Shortly after Dookie's release in 1994, Ernie was removed from the back image. However, 1994 copies of the album are still floating around with the original image on it. Last year, Reddit user PunkPhilosopher1 shared that they found an original 1994 copy that featured Ernie on the back.

Original dookie cover with Elmo. Found this at my uncles house. He doesn’t even care. Doesn’ from r/greenday

Along with the reasons as to why the artwork had to be changed, Armstrong also talked about where and when the back cover photograph was taken.

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"This photo [was] taken in 1993," Armstrong shares. "We opened for Bad Religion at Roseland Ballroom in New York."

Nearly 26 years after the album's release, Green Day's frontman still has a few questions about the back cover art. In his post, he says that he still wonders what happened to one of the people featured in the photo and is asking for an update from anyone that may know.

"I always wondered whatever happened to this girl just to the right of the puppet with short hair," Armstrong asks. "Anyone know?...thought of the day."

So far, no one has commented on Armstrong's post about the mystery girl. In the meantime, next time you happen to be browsing through the used CD section and come across Dookie, take a look at the back and see if Ernie is still hanging out in the crowd.

Do you own a copy of Dookie with Ernie featured on the back cover art? Let us know in the comments below!

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