Former 'Mean Girls' Star's Cameo Leaks in Foreign Release of Reboot

Tina Fey's been trying to downplay the possibility of any major cameos from any of the old "Mean Girls" stars in the rebooted musical -- but unfortunately ... the cat's outta the bag.

!!MAJOR SPOILERS AHEAD ... DON'T READ IF YOU DON'T WANT IT RUINED!!

The new "Mean Girls" hits theaters this Friday here in the States, but a clip circulating online that appears to show a Spanish-dubbed version of the movie -- which has already been released abroad, including in Europe -- is letting fans know early who's back from the past.

As it turns out ... it's Lindsay Lohan, go figure. Indeed, Cady Heron herself is in the new one.

The scene from the movie that's already leaked shows some kind of academic decathlon between students, including the new main character -- played by Angourie Rice. As they're reciting lines/singing ... you can see LiLo serving as the moderator of the contest.

So, she's not reprising her old role, per se, but she does pop up in a fun, quick moment. LiLo also appears to have some dialogue ... commenting on how this feels familiar. Of course, it's all a callback to another big scene from the OG -- aka, "The limit does not exist!"

Lindsay's appearance only seems to last a few seconds ... but it's sure to delight all longtime 'MG' fans. So far, no word of any of the other Plastics having shown up -- not yet anyway.

If you didn't already know -- seriously, how could you not?! -- Lindsay starred as Cady Heron in the original movie -- an innocent teen who goes on a tumultuous journey by Queen Bee Regina George after being initiated into the Plastics at her new high school.

The cameo comes after LL reunited with OG cast member Tina Fey -- who not only wrote the screenplay for the new film but also the musical that came before it. She's also reprising her role as Ms. Norbury in the new flick.

Lindsay's long made her desire for a "Mean Girls" return apparent ... even reuniting with other cast members Amanda Seyfried & Lacey Chabert for an 'MG'-themed commercial for Walmart last year.

But, if you're looking for a serious dose of nostalgia ... head to the cinema Friday cause that's when "Mean Girls" is officially out in the States!