Kourtney Kardashian's Engagement Ring: Kylie Jenner and Kim Kardashian Share First Glimpse

Check out the reality star's impressive new accessory from Travis Barker.

Kourtney Kardashian has a seriously impressive new engagement ring! The reality star said yes when Travis Barker popped the question on Sunday, and her sisters delighted in giving fans a first glimpse at her sizable sparkler.

Travis proposed on the beach in Montecito, California, inside a heart-shaped circle of red roses and candles, as the sun set over the ocean. Later, they celebrated with friends and family at an intimate engagement dinner, where Kim Kardashian celebrated the couple -- and her sister's fancy new hardware.

"KRAVIS FOREVER," Kim captioned a video she posted to of the newly engaged couple to Twitter, along with a diamond ring emoji.

The video Kim posted began on a wide-shot of the pair sharing a kiss, and soon zoomed in on the blindingly brilliant gemstone on Kourtney's hand.

Shortly after, Kylie Jenner took to her Instagram story to share a few photos from the engagement dinner -- including one tightly cropped screenshot showcasing the new ring.

"This oval diamond is spectacular at around eight to 10 carats on a thin pave diamond band, most likely set in platinum, as it will hold the diamonds more securely," Jenny Luker, President, PGI USA Jewelry Inc., told ET of the ring. "Also, since platinum lasts for generations, this ring will likely become an heirloom that Kourtney could pass along to her children. I would estimate this ring costs north of $500,000."

Kylie Jenner/Instagram

source also told ET on Sunday that the pair couldn't be happier about taking this next step in their relationship.

"Kourtney and Travis are over the moon. Getting engaged was always their natural next step and they are so thrilled," the source said. "The proposal was gorgeous and romantic, and everything Kourtney wanted."

"Their families are beyond happy and excited for them too. Their kids are very much looking forward to being an official big happy family," the source added. "Kourtney and Travis really feel like they've found their perfect partner and match. They can't wait for this next step in their journey as a couple and to spend the rest of their lives together."

Kourtney, 42, and Travis, 45, have been longtime friends and neighbors, and started dating in January. The two quickly got serious, taking family trips with their respective kids. Kourtney shares three children -- 11-year-old Mason, 8-year-old Penelope and 6-year-old Reign -- with her ex, Scott Disick. Meanwhile, Travis is dad to two children with his ex-wife, Shanna Moakler -- 17-year-old Landon and 15-year-old Alabama.

A source told ET in May that the couple had discussed a possible engagement and marriage, and that the Kardashian family approves of Travis.