“We are delighted to share that we have named our daughter Sienna Elizabeth Mapelli Mozzi.
“We are all doing well and Wolfie is the best big brother to Sienna,” the tweet said.
Beatrice and her husband, Edoardo Mapelli Mozzi, welcomed their baby daughter at 11.42pm on 18 September.
She is the couple’s first child. Edoardo already has a four-year-old son named Wolfie from a previous relationship with architect Dara Huang.
In an announcement earlier this month, Buckingham Palace said Sienna had been born at the Chelsea and Westminster Hospital in London.
“The baby weighs six pounds and two ounces. The new baby’s grandparents and great-grandparents have all been informed and are delighted with the news.
“The family would like to thank all the staff at the hospital for their wonderful care.
“Her Royal Highness and her child are both doing well, and the couple are looking forward to introducing their daughter to her big brother Christopher Woolf,” the statement said.
Beatrice also shared the news on her Twitter, thanking the midwife team and hospital staff for their “wonderful care”.
Sienna will receive an official title, passed on by her father’s family.
In 2019, Edoardo’s father, Count Alessandro Mapelli Mozzi revealed that all of his son’s future children will receive the title “nobile donna”.
Edoardo, whose official title is Count, comes from a family that was part of the Italian nobility before the country became a republic in 1946.
Speaking to the Mail Online, Alessandro said: “Edoardo is the only male descendant taking the family into the next generation.
“He is a count. His wife will be a countess automatically and any of their children will be counts of nobile donna.”
Beatrice and Edoardo married in a secret ceremony at the Royal Chapel of All Saints in Windsor in July 2020, less than a year after becoming engaged in September 2019.
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