E! News host Maria Menounos and her boyfriend of nearly 20 years, Keven Undergaro, got engaged last Wednesday on-air during Howard Stern‘s SiriusXM radio show. Undergaro got down on one knee and presented Menounos with a one-of-a-kind halo-style engagement ring that features a Signature Stone hidden underneath.

Menounos appeared on the radio show to promote her new book, The EveryGirl’s Guide to Cooking. Just as she had completed her interview with Stern, boyfriend Undergaro, a TV producer, took the microphone, prompting Menounos to ask if he was about to propose. He initially said, "No," but then went on to tell Stern's audience about the emotional ups and downs the couple had experienced over the course of almost two decades.

Then he addressed Menounos directly. "It reminds me just how much I do love you," he said. "And although I said that this isn't a proposal, I want to ask you something, Maria."

"Would you make me the happiest man on earth?" Undergaro asked. "And would you marry me?"

Menounos, 37, was clearly shocked by the surprise proposal, stating, "Are you friggin' kidding me right now? Is this a joke?"

"It's not a joke," Keven replied. "This I wouldn't joke about. I love you so much and this show's meant so much to both of us. Why not make it official now? Will you, honey? Will you accept?"

"Oh, my God! Yes! Yes! Yes! Yes! Of course!" she exclaimed, as she stared at her new ring. "Oh, my God! I can't even believe this is happening."

French jeweler Jean Dousset, whose client list includes Amy Adams and Eva Longoria, dished to PeopleStyle about the details of ring he designed with the assistance of Undergaro.

“The first question I asked Keven was, ‘Has Maria ever said anything about what she would like her diamond cut and ring design to be?’ Every girl does,” Dousset told PeopleStyle. “‘Never in 19 years’,” he replied. That was a first for me. So we imagined what the ring should be based on her personality and style. Bright and chic.”

The ring boasts an Ideal Cut round center stone set in a "Seamless Halo" that is adorned with 220 intricately set brilliant-cut diamonds. The smaller diamonds encircle the center stone and cascade down the band.

"Keven chose to add personal elements to the ring by including a Signature Stone hidden underneath," the designer told E! News. "The choice of color and origin of the stone adds thoughtful detail only he and Maria will know and see." We're assuming the gem is flush-set inside the band.

On Instagram, Menounos posted a photo of her and her boyfriend showing off the new ring. The caption reflected her sheer joy... "omg this happened!!!!!!! thank you @sternshow @bethostern so much for everything. I'm in utter shock! And thank u my love for 19 amazing years. Can't believe we are engaged!!!!"

Images: Screen captures via YouTube/The Howard Stern Show; Instagram/The Howard Stern Show; Getty Images/WireImage/Paul Zimmerman.