Philip has been her ‘rock,’ the man who made her giggle at formal events and helped her to relax when off duty.
The duo’s love story is considered a fairytale come true around the globe.
The couple, both great-great-grandchildren of Queen Victoria, and therefore cousins, first met in 1934 at a family wedding when Elizabeth was eight.
But the dashing Greek prince really captured her heart in 1939 on a visit with her parents to the Royal Naval College in Dartmouth when she was 13.
Handsome Philip, then 18, sealed their friendship over ginger biscuits and lemonade, impressing ‘Lilibet’ and her sister Margaret by vaulting over a tennis net. From that day on, she decided he was 'the one' and, as Philip served in the war, they exchanged letters and met at Windsor Castle when on leave.
After their 1947 wedding and the birth of Prince Charles in 1948, happy times followed as they spent two years living on and off in Malta while he was serving with the Royal Navy’s Mediterranean Fleet.
Despite not seeing much of their young son, who was left in London with nannies, they enjoyed a ‘normal’ life – walking along the seafront arm in arm, holding hands in the back row of a cinema and raring around narrow lanes in a sporty MG.
Practical jokes and Philip’s salty sense of humour were never far away. During a 1951 tour of Canada, he chased his young wife through a train wearing a set of false teeth and, once when he returned from a long naval operation, she greeted him wearing a false beard. They love a laugh, these two!
As she became Queen in 1952, they kept each other’s spirits up with smiles and infinite patience.
When an egg was thrown at their open car during a 1986 visit to New Zealand, Philip got out and simply wiped it off her coat with his handkerchief.
As her Majesty's late Private Secretary Lord Charteris once said: "Prince Philip is the only man in the world who treats the Queen simply as another human being."
When the monarch fell backwards at a Christmas lunch one year at Sandringham after a servant accidentally pulled her chair away, Philip was left in uproarious laughter.
Leading by example, the rock-solid couple have provided an example of a true monarchy love story for their children and grandchildren.
In a 2012 TV interview, Prince William said of his grandparents: "They love it when things go wrong... because obviously everything always has to be right, but when things go wrong around them, they’re the first people to laugh."
Prince Harry said they were "a team" and summed it up perfectly: "I don’t think that she [the Queen] could have done her job without him."