"It's a flawless, beautifully cut diamond stone," Schwartz tells PEOPLE of the ring Barker, 45, gave to Kardashian, 42, when he popped the question at the Rosewood Miramar in Montecito, California on Sunday night.
"I worked on it with Travis and he was a really big part of it," the celebrity jeweler adds. "He was really hands-on in the whole making of it. It's gorgeous and they're happy."
Atiana De La Hoya Instagram. inset: getty
Schwartz is the Kardashian-Jenner family's longtime go-to jeweler (she famously designed Kim Kardashian West's engagement rings from ex-husbands Kris Humphries and Kanye West), so it comes as no surprise that Barker turned to the pro for the special stone.
She's also the woman behind some of Hollywood's most memorable jewelry moments. She designed Blake Lively's custom halo with over 100-carats of champagne diamonds at the 2018 Met Gala, Beyoncé $5 million engagement ring from husband JAY-Z and Angelina Jolie's 115-carat emerald drop earrings at the 2009 Oscars to name just a few.
"Since this is Kourtney's first engagement, it's of course a big deal," the source said. "Most of her family was there to celebrate. Two of Travis' kids were there too. They enjoyed a private, family dinner at the hotel."
"It was a beautiful celebration," added the source. "Everyone is very happy for them. Her family loves Travis."
Barker set the scene for Kardashian on the beach in the middle of a massive heart-shaped floral arrangement surrounded by candles. "Forever," Kardashian captioned photos she shared on Instagram of the special moment.
"It was a complete surprise for Kourtney. Travis told her family that he planned to propose, but everyone was great at keeping it secret," a separate source revealed to PEOPLE. "The Rosewood is their favorite for short weekend getaways. They often stay at the hotel. This is why Travis proposed there. It's a very special place to them, but it was also easier to keep everything a secret by proposing there."
"Kourtney is of course ecstatic," the source added. "She can't wait to marry Travis. She would also love to have a baby with him."
Kardashian shares three children — Mason, 11, Penelope, 9, and Reign, 6 — with ex Scott Disick, 38. Barker was previously married to Melissa Kennedy from 2001 to 2002 and Shanna Moakler, 46, from 2004 to 2008. He shares stepdaughter Atiana, 22, son Landon, 17, and daughter Alabama, 15, with Moakler.