The Queen and Prince Philip appear in a new photo shared on the British Royals' official Instagram page in honour of World Book Day.
The couple are seen in the throwback image in the library of Balmoral Castle in 1976, surrounded by laden bookcases. Philip can be seen smiling as he looks off into the distance, with his arm placed protectively around his wife as she sits at a desk and flicks through a tome.
MORE: Prince Philip has undergone a procedure for heart condition, Buckingham Palace confirms
Along with the photo of the couple, the Instagram post featured a painting of Queen Victoria and Prince Albert in the library at Windsor Castle, with the caption noting that the room is a treasure trove of more than 50,000 books and manuscripts collected by British monarchs over the years.
MORE: Prince Philip told heartbreaking news as he recovers in hospital
A video of the Duchess of Cornwall discussing her love of books as she celebrates the world of literature with authors including Tom Fletcher and Zanib Mian is also included.
READ: Duchess of Cornwall celebrates World Book Day with Tom Fletcher
© Photo: Getty ImagesThe new post came a short time after Buckingham Palace released an update on Prince Philip's condition following his 16th night in hospital.
It was confirmed that the 99-year-old Duke has undergone a successful procedure for a pre-existing heart condition at St Bartholomew's Hospital, and will now remain in hospital for "treatment, rest and recuperation for a number of days".
MORE: The unusual way the Queen orders her meals at Buckingham Palace
This is Philip’s longest hospital stay; he was initially admitted to private King Edward VII's Hospital on 16 February as a precautionary measure after feeling unwell, and on Monday he was transferred by ambulance to St Bartholomew's Hospital in the City of London.
Despite her separation from her beloved husband, the Queen remained upbeat as she took part in her first long-distance video call last week, holding a meeting with government representatives in South Australia.
In a video shared by Buckingham Palace on Monday, the Queen unveiled a new statue of herself remotely, which was recently installed in the grounds of Government House.
On seeing the statue, Her Majesty quipped: "It must be quite alarming to suddenly see it out of the window - you'd think, gracious, has she arrived unexpectedly!"
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