According to the report, the "Cry Me a River" singer-turned-actor asked his actress girlfriend to marry him on the mountains of Jackson, Wyoming some time in late December. "Justin knows how much she loves snowboarding and the mountains, so it was the perfect place," said one source.
The couple had been spotted skiing at the Big Sky Resort in Montana around Dec. 28, a source at the celebrity friendly resort confirms to Billboard.com. Jackson is about a four-hour drive from Big Sky.
Timberlake, 30, and Biel, 29, began dating in 2007; both were coming off long-term relationships with fellow celebrities: he dated Cameron Diaz, his "Bad Teacher" co-star, for three years, while Biel dated actor Chris Evans for five.
In March of 2011, they announced they were parting ways. "The two remain friends and continue to hold the highest level of love and respect for each other," they said.
Several months later they reunited for good, but have kept a typically low profile. During their break, Timberlake concentrated on promoting two films, "Bad Teacher" (June) and "Friends With Benefits" (July).
The pair have not commented on the Us report and there are no immediate details about a wedding.