The two reportedly met during a Pilates session at Equinox gym in Los Angeles where Smith is an instructor.
They went public with their relationship in January and the 34-year-old star of "The Hangover" movies proposed to Smith this month while on vacation at Post Ranch Inn in Big Sur, Calif., UsMagazine.com said.
"They're the cutest couple. She was completely surprised by the whole thing," an insider told the magazine. "The trip to Big Sur, the engagement, the ring, everything. So cute."