"We couldn't be happier," Cooper Hefner tells PEOPLE

The Hefner clan just grew by one!

The late Hugh Hefner's son, Cooper Hefner, is a first-time father to a baby girl, Betsy Rose Hefner. Cooper's wife, Harry Potter actress Scarlett Byrne Hefner, gave birth at 5:23 p.m. local time on Aug. 24, in Los Angeles.

Hefner tells PEOPLE that his little "treasure" weighed 6 lbs., 5 oz., and that he and his wife are "filled with such joy — we couldn't be happier." The baby girl is named after his grandmother, Betsy Aldridge-Conrad, who died in July. "My grandmother meant the world to both Scarlett and I," says Hefner.

“We are overwhelmed with joy to share that our daughter, Betsy Rose Hefner, has arrived. We look forward to being home and spending time together as a family in the days and weeks ahead,” he says.

Cooper Hefner, Scarlett Byrne
Cooper Hefner and Scarlett Byrne Hefner
| Credit: David Becker/Getty Images

The new dad says that his daughter reaffirms his current public service work to build a better world for future generations. Hefner is a fellow for the German Marshall Fund, a teacher and board member at Chapman University and board member of such nonprofits as Children of the Night.

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Cooper Hefner Welcomes Daughter
Betsy Rose Hefner
| Credit: Courtesy Cooper Hefner
Cooper Hefner wedding
Cooper Hefner and Scarlett Byrne Hefner
| Credit: Cooper Hefner/Instagram

Cooper, 28, and Scarlett, 29, revealed their baby news in March, with the then-dad-to-be sharing a photo of his wife smiling while sitting in a field of grass with her hands placed below her baby bump.

Also included in the post was a sweet video of the pair walking hand-in-hand as they took part in a romantic stroll along a beach.

"Scarlett and I have been blessed with wonderful news we are ecstatic to share. This summer we will be welcoming a new member to the family," wrote Cooper at the time. "The two of us could not be happier as we wait for the arrival of our little one."

Scarlett — who played Pansy Parkinson in the Harry Potter franchise films Half-Blood Prince and Deathly Hallows: Part 1 and Part 2 — also shared the exciting news with the same photo, captioning it, "Cooper and I are delighted to share that we have a little one on the way."

"Our hearts are filled with gratitude and joy, and the two of us can't wait to meet the newest little Hefner," she added.

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The couple tied the knot in November 2019. Cooper announced their nuptials on social media alongside a photo of the couple at the Ventura County courthouse in California.

"Scarlett and I have made it officially legal and the two of us could not be happier," he captioned his post, which also included a slideshow of photos of the pair over the years. "Cheers to a life full of love, happiness, adventure, and great purpose, Mrs. Hefner."

"I love you dearly and very much look forward to planning our wedding celebrations in the months ahead," he added. "I love you, Scarlett."

Scarlett also posted about the news, captioning the same courthouse photo of the pair in part, "Cooper and I are excited to share that we legally married. We are looking forward to planning our wedding in the coming months where we will celebrate further with our friends and family."

"I love you Cooper," she added. "I am proud to stand by your side, as your partner, your friend, and your wife. I cannot wait to continue building a life together. My heart is so full and I am so grateful for our love."