Credit: Fern/Splash News Online

Miley Cyrus and Liam Hemsworth are definitely back on.

The two locked lips Monday morning in her Mercedes Benz SUV in Los Angeles.

On Saturday, they were spotted together at Cyrus' Toluca Lake, Calif., house before hitting a Panera Bread shop and Starbucks.

Cyrus, 17, and Hemsworth, 20 -- who announced their split last month -- are dating again, a source close to the couple confirms to UsMagazine.com.

"She got back from Paris and they reunited," says the insider.

Despite being photographed with her LOL costar Douglas Booth, the source says he and Cyrus are "just friends."