Say it isn't so!

Miley Cyrus' fiance Liam Hemsworth has apparently betrayed his lady love with none other than January Jones!

The Hunger Games actor and the Mad Men actress got cozy at a Grey Goose pre-Oscar bash, according to Life & Style.

The pair supposedly enjoyed a steamy makeout sesh!

"They went to a private house party, and right in the middle of the party, January was clinging to Liam, saying, 'You're so handsome.' He kept saying, 'We can't do this here.' Then they left holding hands and went out in the hallway and were making out. She was wasted. It wasn't good," a source tells the mag.

So how does the Hannah Montana star feel about the rumored infidelity?

"Miley is freaking out. She's been telling her friends that she trusts him but if she finds out the cheating claims are true, the engagement is over," the source adds.

This doesn't sound good!