Palace shares rare photo of Queen Elizabeth II, Prince Philip amid news of duke's recovery

Queen Elizabeth II and Prince Philip appeared youthful in a throwback photo that Buckingham Palace shared on Thursday to commemorate World Book Day.

The British monarch is barely recognisable in the picture which was captured in the library at the Balmoral Castle in 1976. Born in 1926 and 1921, the Queen and the Duke of Edinburgh would have been 50 and 55-years old, respectively, in this picture.

The photo shows Queen Elizabeth II seated at a desk with a book in hand while Prince Philip stood by her side. Both are not looking directly at the camera. Behind them are rows of books collected over the years by the royal family.

"Happy #WorldBookDay. The Queen and The Duke of Edinburgh are pictured in the Library at Balmoral Castle in 1976," reads the caption on the photo shared on Twitter.

The palace also shared a throwback artwork of Queen Victoria and Prince Albert at the massive library at Windsor Castle. The Royal Library is a "treasure trove of more than 50,000 books and manuscripts gathered by the British monarchs over the centuries."

Buckingham Palace released the photos to celebrate World Book Day, an initiative that aims to tackle illiteracy by giving a book to every child and young person. The pictures came at the heels of news about Prince Philip's health after he was transferred to St. Bartholomew's Hospital in London to undergo surgery for a pre-existing heart condition.

A palace spokesperson said the 99-year old duke had a successful operation and that he is resting and recovering. However, he will remain in the hospital for further treatments and for "rest and recuperation for a number of days." A prior announcement revealed that the Duke of Edinburgh will be in the facility at least until the end of the week.

Royal fans are delighted to hear about Prince Philip's successful procedure and thanked the palace for the throwback photo of him and Queen Elizabeth II.

"I'm so happy that all went well for Prince Philip during his operation and our love remains with him for a full recovery. May he be home with his loved ones soon," one fan wrote and another commented, "Beautiful photo for World Book Day, All my best wishes for the Duke of Edinburgh during his stay in hospital recovering & my thoughts to Queen Elizabeth ll."