Kourtney's ex is 'not happy at all' with the new development in her love life.
Scott Disick, Kourtney's ex and the father of her three children, isn't jumping for joy at the engagement news, a source tells ET.
"Scott is stewing over Kourtney and Travis' engagement and not happy at all," the source says. "He's lonely right now and not in a relationship, and is very jealous that things are working out for Kourtney. Scott would prefer to go back to when him and Kourtney were just getting along as co-parents without anyone else in their lives romantically."
Kourtney and Scott continue to co-parent their three kids, Mason, 11, Penelope, 9, and Reign, 6, despite their sometimes strained relationship.
"He's trying to figure out his next move when it comes to their kids," the source says. "Kourtney is trying to ignore any negativity from Scott because she has been down that road too many times to count and is just enjoying this moment."
During the Keeping Up With the Kardashians reunion special in June, Scott gave Kourtney his blessing for her relationship with Travis.
"I think if you really love somebody, you want them to be happy no matter what," he shared at the time. "So I do give her a blessing to be happy."
Things went south in September when Scott was called out by Kourtney's other ex, Younes Bendjima, for allegedly DMing him disparaging comments about Kourtney and Travis' PDA-filled vacation.
"Kourtney and Scott are definitely not as close as they once were. Scott has some unsettled ill will towards Kourtney and Travis being together and Kourtney is over the jealousy," another source told ET. "She thinks Scott needs to grow up."
Meanwhile, Scott has seemingly remained close with the Kardashian family. Earlier this month, he was spotted attending the Saturday Night Live after-party with Khloe Kardashian on his arm following Kourtney's sister, Kim Kardashian West's, hosting gig.
Travis proposed to Kourtney over the weekend on a rose-covered beach in Montecito, California, and while Scott might take issue with the engagement, the rest of the family seem thrilled.
"Their families are beyond happy and excited for them," a source told ET. "Their kids are very much looking forward to being an official big happy family."