Sarah Ferguson became a grandmother to a baby girl for the first time when Princess Beatrice welcomed her daughter on Sept. 18.

Beatrice and her husband Edoardo finally shared the name, Sienna Elizabeth, this past Friday. The middle name is a clear tribute to The Queen, but there's another more subtle family tribute in the first name, Sienna.

How Princess Beatrice honoured Sarah Ferguson in baby name

Sienna's name came about because the couple wanted an Italian name, given Edoardo's heritage. But they also wanted to recognize the baby's grandmother Sarah.

So, a source told Hello!, Beatrice and Edoardo chose "an Italian name which started with an S for Sarah, to honour the Duchess [Sarah Ferguson]."

There's another reason they wanted to pay tribute to Fergie, too. The source said that the new baby shares "the golden rust colour of both the Duchess's hair colour and Beatrice's."

So little Sienna is another royal redhead, just like her mother Beatrice and grandmother Sarah. She's now 2 weeks old.

Beatrice and Edoardo revealed the name of their daughter on Friday, in social media posts with a photo of her footprints. 

"Our life together has just begun, and I can't wait to see all the amazing things that await us," wrote Edoardo, who is now a father to the baby girl in addition to a son, Wolfie, from a previous relationship.

On Twitter, Beatrice added: "We are all doing well and Wolfie is the best big brother to Sienna."

Beatrice's daughter stands 11th in line to the British throne, and she's the 12th great-grandchild of Queen Elizabeth.