Sadie Bomar confirmed the news to Gossip Cop, saying, "He called me on Christmas Day and told me he's engaged." She added that her superstar grandson gave her strict orders to keep quiet "until after the holidays."
Bomar added that she's "so happy" for the couple and that Biel has her thumbs-up. "The family loves Jessie," she said. "She's a very sweet girl."
Despite earlier reports that the two had gotten engaged in Wyoming, Bomar said they were actually in Montana at the time. Sources told People magazine that the twosome were in Big Sky Country vacationing when he asked her to marry him with a "custom-designed" ring.
Bomar has been making the media rounds since the news broke Wednesday. She also confirmed the engagement to "The Wendy Williams Show," saying "she's very excited for them."
Timberlake and Biel began dating in 2007 and broke up briefly in 2011 before getting back together later that year. In 2011, Timberlake opened up a bit about his feelings for Biel to Vanity Fair. "She is the single-handedly most significant person in my life. In my 30 years, she is the most special person, OK?" he said. "I don't want to say much more, because I have to protect things that are dear to me — for instance, her."
When asked about having to deal with all the attention the pair have received over the years, Biel told Vogue, "I don't want to talk about it. I don't feel the need to clear anything up. It's the most precious thing that I have in my life, and I care about it so much that I don't care about what anyone says or thinks. I have just not addressed it in any real way, and I'm not going to. It's mine. And I really like that about it."