Grande then ran off the stage before quickly recovering and launching into a performance of her song, NASA.
Grande's fans were outraged at the fruity attack, taking to Twitter to vent their anger … and share conspiracy theories as to who was behind it.
One name who came up? Beyonce.
An Ariana fan wrote: "Throwing a lemon at Ariana Grande? How dare you."
Another asked: "Which one of y'all Beyonce stans threw a lemon at Ariana Grande?"
A third said: "A f*** you to the person who threw that lemon at Ariana."
The incident came after it was reported that Grande was paid $AUD 8 million to headline Coachella in the Sunday night slot, which was said to be "double" what Beyonce was paid for her epic 2018 gig.
However, The Blast later revealed that Beyonce had actually been paid about the same for each of the two Coachella weekend performances.
Grande has not yet commented on lemon-gate.
Meantime, the New York-based singer opened up about the toll her Sweetener tour is taking.
After one fan speculated about Grande not spending as much time on social media, she responded that she doesn't "have anything" to give her fans.
"I just feel empty and i wanna have more to say / better energy to give to u and rn i don't have anything. love u," Grande wrote.