Sarah Ferguson Reveals Adorable Nickname for Granddaughter Sienna — Who Is a 'Mini Beatrice'

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Princess Beatrice of York (L) and Sarah Ferguson, Duchess of York
Princess Beatrice of York (L) and Sarah Ferguson, Duchess of York

David M. Benett/Getty

Sarah Ferguson has a sweet name for her granddaughter Sienna Elizabeth!

The Duchess of York, 63, appeared at The 92nd Street Y, New York on Monday night to discuss her new novel A Most Intriguing Lady on the eve of the book's release. She spoke about her confidence as a second-time novelist, her relationships with the royal family and relishing in her role as a grandmother — plus what she calls Princess Beatrice and Edoardo Mapelli Mozzi's baby girl, 1.

"What is it like to be a grandmother? Talk us through that," moderator Samantha Barry asked.

"I love seeing my girls, who are exceptional. Full stop, they're exceptional," Sarah said of Beatrice, 34, and Princess Eugenie, who shares son August Philip Hawke, 2, with husband Jack Brooksbank.

"Then on top of that, these two little, baby Eugenie, baby Beatrice, they're looking at me with the big eyes. They look like my girls," she said of her grandkids. "August is teaching me to play trains and diggers. And Sisi is just mini Beatrice, and she gets little pink tutus, cause Beatrice likes to dress her up like Barbie."

RELATED: Sarah Ferguson Says She and Princess Diana Would Have a 'Granny-Off': 'She Would Run Faster in the Races'

Sarah Ferguson Rollout
Sarah Ferguson Rollout

Sarah Ferguson Instagram Princess Beatrice, Sarah Ferguson and Princess Eugenie

August and Sienna were both born in 2021, and the family will expand again this summer when Eugenie and Jack's second baby is born. In January, Buckingham Palace announced that the princess was pregnant.

"Princess Eugenie and Mr. Jack Brooksbank are pleased to announce they are expecting their second child this summer," the palace said in the announcement. "The family are delighted and August is very much looking forward to being a big brother."

The Duchess celebrated the news of Eugenie's pregnancy with an Instagram tribute, where she similarly shared a nickname for her younger daughter's son.

Sarah Ferguson
Sarah Ferguson

David M. Benett/Dave Benett/Getty, Sarah Ferguson/instagram

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"You will be sharing puddles, Augie!" Fergie wrote alongside a photo of her grandson playing in a puddle while wearing a yellow raincoat. "Superb news, Granny heaven…. So deeply grateful."

The baby on the way will be the third grandchild for the author, who shares Eugenie, 32, and Beatrice with her ex-husband, Prince Andrew. Beatrice is also a stepmother to Christopher Woolf, affectionately known as Wolfie, who Edo shares with his ex Dara Huang.

The Duchess tells PEOPLE exclusively in this week's issue that she's savoring life with her grandchildren, who "just follow me around like Peter Pan."

"I'm 'Super Gran Pan!' " she says, adding that the little ones "think I'm very funny."

Sarah Ferguson Rollout
Sarah Ferguson Rollout

Zoe McConnell Sarah Ferguson

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Becoming a grandmother came naturally to the longtime children's book author, whose bestselling Budgie the Little Helicopter series became a popular animated show and whose enduring Little Red character also inspired a series of books. She also hosts a YouTube series for children, Storytime with Fergie and Friends.

"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," Sarah says.