LeAnn Rimes angagement photoIs LeAnn Rimes engaged? Not exactly.

Over the weekend, Rimes' boyfriend, actor Eddie Cibrian, tweeted this photo of him kneeling while a shocked Rimes looks on.

"I couldn't resist..." he tweeted Sunday evening.

But sources tell PEOPLE the photo was just a joke. "They are not engaged," says a source close to Rimes. "It was just part of the Halloween fun."

Rimes and Cibrian met and began a relationship while filming the 2008 Lifetime television movie 'Northern Lights.' Both were married at the time but have since divorced their spouses to be together. She ended her 7-year marriage to Dean Sheremet, admitting in June that they worked on their relationship after her infidelity became public but decided "it wasn't a marriage that fulfilled either one of us."