The Blink-182 drummer, 45, went down on one knee on Sunday, on the beach in Montecito, California. He had set up an enormous arrangement of roses and candles in the sand, which surrounded the couple as he proposed. The pair have been together since 2020.
Kardashian, 42, was wearing a black dress with black nail varnish and Barker was in black jeans and a black and white striped top.
This is Kardashian's first engagement. She has three children, Mason, 11, Penelope, 9, and Reign, 6, with her ex Scott Disick, with whom she had an on-and-off relationship between 2007 and 2020. Disick was a regular on the family's reality TV show. Barker has been married previously, to Melissa Kennedy, from 2001 to 2002 and Shanna Moakler from 2004 to 2008, with whom he has two children, Landon, 17, and Alabama, 15, and one stepdaughter, Atiana, 22.
Kourtney Kardashian's oval-cut engagement ring
Barker's daughter Alabama shared a close-up of the ring on her Instagram Story, writing, "So happy for you guys I love u both".
The ring is a large oval-shaped diamond, set on a thin white gold or platinum band designed by celebrity jeweller Lorraine Schwartz.
"It's a flawless, beautifully cut diamond stone," Schwartz told People magazine. "I worked on it with Travis and he was a really big part of it. He was really hands-on in the whole making of it. It's gorgeous and they're happy."
Schwartz also designed Kim Kardashian West's engagement rings from both ex-husbands Kris Humphries and husband Kanye West, who has now legally changed his name to just Ye.
Jeweller Mehul Pethani from Cara Jewellers in Dubai estimates that the diamond is between eight and 10 carats. To buy the ring in the UAE, it would cost Dh600,000 to Dh1.5 million ($163,000 to $408,000), depending on cut and clarity.
Barker is not the first celebrity to pick an oval engagement ring, a host of high-profile women sport the elegant rock shape.
Jewellers Rogers & Hollands describe people who opt for oval diamonds as "known for having a creative spirit," saying that they are "individualistic, daring and bright".
The shape, introduced by diamond manufacturers Lazare Kaplan in the 1960s, is a flattering one for an engagement ring, as they create the illusion of elongated fingers.
When Ariana Grande got engaged to Dalton Gomez in December 2020, he presented the singer with an oval diamond set on an axis alongside a single pearl. Justin Bieber proposed to now-wife Hailey Bieber with an oval-cut solitaire diamond by Solow & Co, and Blake Lively's engagement ring is an oval pink diamond ring by Lorraine Schwartz.