Princess Beatrice has given birth to her first child, a daughter, Buckingham Palace has announced.
The baby was born at the Chelsea and Westminster Hospital in London at 23.42 on Saturday night, weighing 6lb 2oz.
A palace spokesperson said the Princess and her husband, Edoardo Mapelli Mozzi, were "delighted" to announce the safe arrival of their daughter.
The statement added: "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 Princess, 33, was admitted to the hospital on Friday, with Mr Mapelli Mozzi, 38, at her side.
The newborn is the Queen's 12th great-grandchild, and the fourth born this year.
She will be 11th in line to the throne.
The baby is a second child for Mapelli Mozzi, whose has son Christopher - known affectionately as Wolfie - from a previous relationship with Dara Huang, an American architect.
The pair were engaged before separating in 2018.
Wolfie acted as best man and page boy when his father and Princess Beatrice wed last July and Beatrice recently revealed that she considers her stepmother role "an honour".
She said she refers to the 5-year-old as her "bonus son," a relatively new way of describing such a relationship that is considered warmer than "stepchild" or "step-parent".
Princess Eugenie, Beatrice's younger sister, shared her congratulations on Instagram, writing: "To my dearest Beabea and Edo Congratulations on your new angel. I can't wait to meet her and I'm so proud of you. We're going to have so much fun watching our children grow up. Love Euge."
In a separate message, she added: "To my new niece I love you already and think you're just awesome from the photos.. we're going to have so much fun together. Love your Auntie Euge."
Buckingham Palace announced in May that Beatrice and Mapelli Mozzi were expecting a baby this autumn.
The new baby is the second grandchild for the Duke of York and his former wife, the Duchess of York, following the birth of Princess Eugenie and Jack Brooksbank's son, August Philip Hawke Brooksbank, on February 9.
The Duke, who is preparing to fight a civil lawsuit after being accused of sexual assault, is currently at Balmoral, the Queen's Aberdeenshire estate, where he is expected to remain.
The Duchess, who travelled with him to Scotland earlier this month, is understood to have returned to their Windsor home on Friday and met her new grandchild over the weekend.
A friend of the family said: "She is absolutely over the moon."