The Queen’s granddaughter and her husband Edoardo Mapelli Mozzi are “very pleased” to be welcoming their first child, the Palace said.
The news has brought joy to the monarch and the royal family who are mourning the loss of the Duke of Edinburgh who died last month.
The Palace said: “The Queen has been informed and both families are delighted with the news.”
Beatrice, 32, and Mr Mapelli Mozzi wed last July in a secret lockdown wedding attended by the Queen and Philip after their planned ceremony was postponed because of the pandemic.
The baby will be the Queen’s 12th great-grandchild following the arrival of the Sussexes’ second child in the summer.
Beatrice’s younger sister Princess Eugenie, to whom she is incredibly close, welcomed a baby boy, August, in February.
The sisters will be delighted to have their children so close together in age, and to share the experience of being first-time mothers.
Their cousin Zara Tindall welcomed her third child, a son Lucas, in March, while Harry, also their cousin, and Meghan, will welcome a daughter in the next few months.
Beatrice is already stepmother to Mr Mapelli Mozzi’s young son Wolfie, from his previous relationship with his ex-fiancee Dara Huang.
Known as Edo, Mr Mapelli Mozzi is a millionaire property tycoon and the son of former Olympic skier Count Alessandro Mapelli Mozzi and Nikki Williams-Ellis.
Beatrice was last seen at a royal event at the funeral of her grandfather Philip on April 17 wearing a mask and belted black coat, as the Windsors gathered for a socially distanced final farewell to the royal patriarch.
The princess is the eldest daughter of the Duke of York and Sarah, Duchess of York.
Ninth in line to the throne, she will move to 10th place when the Sussexes’ baby arrives.
The princess’s son or daughter will be 11th in line to the throne.
Beatrice is not a full-time working royal and is vice president of partnerships and strategy at Afiniti, an artificial intelligence software firm.
She has a number of royal patronages including the Forget Me Not Children’s Hospice, the Teenage Cancer Trust and the Helen Arkell Dyslexia Centre.