Justin Timberlake, Jessica Biel engaged?

NEW YORK - FEBRUARY 18: (L-R) Jessica Biel and Justin Timberlake attend the Paris68 Fall 2010 Fashion Show during Mercedes-Benz Fashion Week at Milk Studios on February 18, 2010 in New York, New York. (Photo by Astrid Stawiarz/Getty Images) *** Local Caption *** Justin Timberlake;Jessica Biel
Astrid Stawiarz
Jessica Biel and Justin Timberlake attend the Paris68 Fall 2010 fashion show during Mercedes-Benz Fashion Week on Feb. 18, 2010, in New York.

(CBS) Are Jessica Biel and Justin Timberlake ready to make it official?

Pictures: Justin Timberlake
Pictures: Jessica Biel
Pictures: Celebrity weddings and engagements The on-again, off-again couple has been making headlines this week ever since Us Weekly cited sources who say Timberlake popped the question while vacationing in Jackson, Wyo. in late December.

The stars' reps haven't confirmed the report, but an insider tells Us Weekly that Timberlake, 30, has "never been happier" with Biel, adding, "He knew it was the right time to propose."

Aside from a brief split in 2011, Biel, 29, and Timberlake have been together for more than four years. "When they reunited, they had a conversation about taking the next step," another insider said.

Now there are reports that Timberlake's grandmother Sadie Bomar has spoken up. She reportedly told Gossip Cop, "He [Timberlake] called me on Christmas Day and told me he's engaged," noting that her grandson asked her not to say anything "until after the holidays."

Engagement reports first started to crop up before the holidays, but there's still no official word from either of the lovebirds.

Timberlake started dating Biel in 2007, shortly after breaking it off with Cameron Diaz.