We have a baby Sienna update.

Princess Beatrice and Edoardo Mapelli Mozzi welcomed their baby girl back in September. The couple is now mailing replies to fans who congratulated them after the birth, and the message reveals a cute nickname for Sienna.

Princess Beatrice's nickname for her daughter Sienna is...

In the card, Beatrice and Edoardo call their daughter "Little Rockstar." How cute!

The card was shared by Royal Replies on Instagram, and it has an image of newborn Sienna's footprints on the front.

The thank-you reply in full reads: "Sienna Elizabeth: 18. 09. 2021. Thank you so much for thinking of us at this remarkable and special time.

"We are so thankful to have welcomed this little person into our family. She is a Little Rockstar!" The card is signed "with love: Beatrice, Edo, Wolfie & Sienna."

Born on Sept. 18, Sienna Elizabeth Mapelli Mozzi is now 4 months old. We have yet to see a first photo of the royal baby.

A great-granddaughter of Queen Elizabeth II, Sienna is 11th in line to the British throne.

Sienna is the first child for Princess Beatrice, and the second for her husband Edoardo. He has a son named Christopher (a.k.a. Wolfie) from an earlier relationship.

So it looks like it's Wolfie and Little Rockstar now.