Queen Elizabeth became a great-grandmother for the first time when the wife of her grandson Peter Phillips gave birth to a baby girl, Buckingham Palace said on Thursday.
Autumn Philips, a Canadian, gave birth on Wednesday.
"The Queen, The Duke of Edinburgh, The Princess Royal, Captain Mark Phillips and Autumn's family have been informed and are delighted with the news. The baby's name will be confirmed in due course," the statement said.
The baby is 12th in line to the throne.
Her birth also made Peter Phillips's sister Zara an aunt. The royal family said last week that Zara, a successful equestrian athlete, was to marry rugby player Mike Tindall.
Peter and Autumn Phillips, who courted controversy by selling the rights to their wedding to Hello! magazine for a reported 500,000 pounds, live in Hong Kong, where he works for the Royal Bank of Scotland.