This is one messy MTV love triangle.

The night before Siesta Key returns for a third season, Juliette Porter accused costar Cara Geswelli of cheating on her boyfriend Garrett Miller with fThe Challenge’s Johnny “Bananas” Devenanzio.

“Cara is a shady skank and she f*ckrd @johnnybananas while dating @__GarrettMiller in Cancun,” Porter, 21, tweeted on Monday.