LONDON (AP) — Britain's Queen Elizabeth II and Prince Philip will celebrate their 73rd wedding anniversary Friday, and for the occasion the royal couple have released a photograph of themselves opening a card from three of their great-grandchildren.

The photo made public late Thursday shows Britain's longest-reigning monarch and her husband seated on a sofa at Windsor Castle, examining the card made by the children of their grandson Prince William and his wife, the Duchess of Cambridge. The card features a pop-up number 73.

Elizabeth was only 21 when she married Royal Navy Lt. Philip Mountbatten at Westminster Abbey on November 20, 1947. She has been queen since 1952, ruling longer than any other British monarch.

Her marriage to Prince Philip is also the longest for any British sovereign.

While Queen Elizabeth continues to carry out her duties, Prince Philip, 99, has retired from public life. With England under a national lockdown to control the COVID-19 pandemic, the couple is self-isolating at Windsor Castle.