Miley Cyrus' relationship with Liam Hemsworth is reportedly in crisis after the We Can't Stop singer's recent antics.

On Sunday, she made headlines for twerking and grinding against singer Robin Thicke as they performed Blurred Lines at the 2013 MTV Video Music Awards. Leaving little to the imagination, Cyrus danced around stage in a nude bra and bootie shorts, as she stuck out her tongue suggestively.

Missing out on the evening's highlight performance was Cyrus' fiance -- who has been M.I.A. ever since Sunday night. New reports claim Hemsworth is "mortified" by Cyrus' raunchy behavior.

"Liam really does care about Miley, but her racy new look and sort of ghetto attitude isn’t exactly what he signed up for," a pal told Radar.

Robin Thicke 'Bummed' After Miley Cyrus 'Blurred Lines' VMAs 2013 Performance 

The pair have had a rocky romance -- and this may have been the final straw for Hemsworth, who asked Cyrus to marry him in June 2012 with a 3.5-carat diamond ring.

"It’s pretty much over. He knows he can’t stay with her when this is who she’s become," the source concluded. "He doesn’t want to babysit her anymore. He has to move on."

Hemsworth and Cyrus were last seen together at the Aug. 8 premiere of Liam’s new film Paranoia. According to Us Weekly, the couple were anything but lovey-dovey.

"Miley and Liam acted like they didn't even know each other the entire night," the source said. "She was wearing her ring but they acted as if they were strangers."

Watch Miley Cyrus and Robin Thicke perform Blurred Lines at the 2013 MTV Video Music Awards: