Sarah Ferguson Says She's 'So Proud' of Daughters Beatrice and Eugenie on U.K. Mother's Day

David M Benett/Dave Benett/Getty Images Princess Beatrice, Sarah Ferguson and Princess Eugenie

Sarah Ferguson has much to celebrate on the U.K.'s Mother's Day.

The Duchess of York, 63, marked the annual holiday, which is known as "Mothering Sunday" and celebrated in the U.K. this year on March 19, with a tribute to her daughters Princess Beatrice and Princess Eugenie, sharing a throwback to Instagram of the two of them as kids.

"I'm so proud of my girls and the beautiful women and mothers they have grown up to be," wrote Ferguson in the caption. "I feel extremely blessed to call them mine. My darlings, you are my sunshine always & forever. #happymothersday"

RELATED: Sarah Ferguson on Her 'Granny' Era: 'They Follow Me Around Like Peter Pan'

Ferguson became a grandmother for the first time when Eugenie, 32, and husband Jack Brooksbank, who are expecting their second baby this summer, welcomed 2-year-old son August Philip. Beatrice, 34, and husband Edoardo Mapelli Mozzi, meanwhile, welcomed their first child, Sienna Elizabeth, 18 months, in 2021.

In a post on her own Instagram page, Eugenie shared a photograph of herself and her son, captioning it, "I love being your Mumma! Happy Mothers Day! Xx."

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Ferguson celebrated Eugenie's baby news in January, captioning one post, "You will be sharing puddles, Augie! Superb news, Granny heaven…. So deeply grateful.

In another, which featured a photo of herself hugging her daughter, the proud mom said, "So happy for my girlie."

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Ferguson said that her grandchildren "look like my girls" as she appeared earlier this month at The 92nd Street Y in New York City.

"August is teaching me to play trains and diggers," said Ferguson. "And Sisi is just mini Beatrice, and she gets little pink tutus, cause Beatrice likes to dress her up like Barbie."

Chris Jackson/Getty Sarah Ferguson with Princess Beatrice and Princess Eugenie

The Most Intriguing Lady author previously told PEOPLE that her grandchildren "think I'm very funny" and "just follow me around like Peter Pan," adding: "I'm 'Super Gran Pan!'"

"Everyone says, 'Oh, has it changed your life?' And I go, 'No, because I live [in the mindset of] 3- to 6-year-olds.' So I've now got another audience that likes me," said Ferguson, a longtime children's book author and host of YouTube's Storytime with Fergie and Friends.

RELATED VIDEO: Sarah Ferguson on What She Told Daughters Beatrice and Eugenie Growing Up: 'I've Already Made Those Mistakes'

Ferguson also became mother to a few furry faces when she and ex-husband Prince Andrew took over care for Queen Elizabeth's corgis, Sandy and Muick (pronounced "Mick"), after the beloved monarch died at age 96 in September.

"They are national icons, so every time they run chasing a squirrel, I panic," the Duchess told PEOPLE. "But they're total joys, and I always think that when they bark at nothing, and there's no squirrels in sight, I believe it's because the Queen is passing by."