Credit: Dimitrios Kambouris/FilmMagic

After a series of breakups and makeups, Justin Timberlake and Jessica Biel have finally decided to get married!

Several insiders tell the new issue of Us Weekly (on stands Friday) that the couple of four and a half years became engaged in late December.

Timberlake, a six-time Grammy winner, popped the question to Biel, 29, in the mountains of Jackson, Wyoming. "Justin knows how much she loves snowboarding and the mountains, so it was the perfect place," one insider explains.

After a brief three-month split in 2011, Biel made it clear that she wanted to spend her life with Timberlake, 30. "When they reunited, they had a conversation about taking the next step."

Another Timberlake insider adds that he's "never been happier" with the New Year's Eve actress. "He knew it was the right time to propose."

For more details on the couple's engagement -- including how Timberlake and Biel broke the news to friends and family -- pick up the new issue of Us Weekly, on stands Friday!