Naya Rivera may be happily married, but sources are saying that her ex-fiance Big Sean dating Ariana Grande is her "worst nightmare."

HollywoodLife reports that Rivera, 27, has been very upset about the relationship rumors. And though she flashed a smile at a Justin Timberlake, she was hiding her feelings.

"Naya was trying to keep it together and have fun at the concert but she was really upset because of the news about Sean and Ariana," a source said. "She kept bringing it up."

It seems Grande was a source of discussion and disagreement when the two dated.

"It's her worst nightmare because she was always very sure that Sean was cheating on her with Ariana, they fought about that a lot," the source added. "Sean would tell her she was crazy and jealous, he swore to her that Ariana was just a friend, he even said she was like a little sister. Naya feels like this is proof that she was right all along and Sean was hooking up with Ariana. She doesn't want him back, but it's still a huge wound and she's hurt and she's angry."

The ex-couple, who originally met on social media, did not end on good terms.

The engagement was off abruptly, and she later took to Twitter to call him a thief.

"@bigsean Stealing Rolexes from a lady's house now," she said. "Maybe cuz I'm on Glee and making more money or something #triflin."

She also married very quickly after breaking up with Big Sean. In fact, she and Ryan Dorsey married on her original wedding date.

Big Sean and Grande's relationship has not been confirmed.

Although an eyewitness said the two were kissing during a movie, neither Big Sean or Grande has admitted to being in a relationship.