The Queen may have well felt the absence of Prince Philip on her open carriage ride through London streets to Buckingham Palace, held to mark the end of celebrations for the diamond jubilee weekend. The Duke of Edinburgh has rarely missed a public appearance alongside his wife over the last 60 years of her reign. Indeed, just as the Queen herself is now the second longest serving British monarch, Prince Philip, who turned 91 on 10 June, is now the oldest serving spouse of a reigning British monarch.

Unfortunately, Prince Philip was admitted to the King Edward VII Hospital for treatment of a bladder infection, just as last weekend's diamond jubilee celebrations came to an end. As testament to how close the Queen and Prince Philip are, Princess Eugenie said in a television interview that his absence would have made the last two days of the weekend celebrations quite "testing" for her grandmother.

"To see Granny and Grandpa standing for four hours, I mean, together, they are invincible. They are the most incredibly supportive couple to each other. Grandpa was unfortunately taken ill and for Granny to come and do that alone was probably quite testing. He is her rock really and she is his," the 22-year-old princess told Sky News.

Fortunately, the prince made a good recovery and was released from hospital in time to be home with his family for his 91st birthday.

The Queen and Prince Philip have been together for over 65 years, since their engagement was announced in July 1947, when the Duke of Edinburgh was Lieutenant Philip Mountbatten and the Queen was still Princess Elizabeth. Their royal wedding took place in Westminster Abbey on 20 November the same year. Since the Queen's coronation and accession to the throne in 1953, Prince Philip has had crucial roles in various aspects of national life, along with the Queen.

Their marriage has proven to be a role model for several couples, including those within the royal family. Unfortunately, their own children have had less stable marital lives. With the exception of their youngest child, Prince Edward, their three other children - Prince Charles, Princess Anne and Prince Andrew - have all had divorces.

IB Times UK has compiled a pictorial tribute to the prince for his 91st birthday.