Longtime pals Zac Efron and Rumer Willis are taking their relationship to the next level, an insider tells Star. They celebrated their new status with a romantic Turks & Caicos getaway in late December.

"Zac had been trying to win back High School Musical costar Vanessa Hudgens, but she's moved on" with Austin Butler, as Star revealed.

Zac, 24, finally realized that the right woman had been there for him all along. "At first, they'd socialize in groups, then Rumer started going over to Zac's L.A. house," says the insider. "She'd decorate and make the place really home — then she began spending the night, and they're acting like a couple. Zac told Rumer he's developing strong feelings for her."