On Twitter, The Royal Family account released a photograph to mark her birthday, showing the Queen with two ponies.
“Taken last month in the grounds of Windsor Castle, The Queen is pictured with two of her fell ponies, Bybeck Katie and Bybeck Nightingale,” the account said.
A BBC report said Britain’s longest-lived monarch had travelled by helicopter to her Norfolk estate and is expected to stay in a cottage on the estate particularly liked by her late husband, Prince Philip.
The Queen was in Sandringham earlier this year when she marked her accession to the throne in 1952.
Birthday wishes have been sent by Prime Minister Boris Johnson and Labour leader Keir Starmer and gun salutes will be fired.
A Barbie doll celebrating the legacy of the Queen is being released to commemorate her Platinum Jubilee, featuring a recreation of her wedding tiara and an ivory gown fitted with a blue ribbon.
