They are one of the world's most famous couples, but what do the Queen and Duke of Edinburgh think of one another?
In their own words, here are some quotes from the Queen and her consort.
:: The Queen on Philip
"How good he is, Crawfie. How high he can jump." - To her nanny about Philip as she watched him jump over the tennis nets at Dartmouth College during their first publicised meeting in 1939.
"Oh Philip, do shut up. You don't know what you're talking about." - When the Duke was sounding off on a subject on the Royal Yacht Britannia.
"If I am asked what I think about family life after 25 years of marriage, I can answer with equal simplicity and conviction, I am for it." - Silver wedding anniversary speech in 1972.
"All too often, I fear, Prince Philip has had to listen to me speaking." - On their golden wedding anniversary in 1997.
"Frequently we have discussed my intended speech beforehand and, as you will imagine, his views have been expressed in a forthright manner." - Again in 1997
"He is someone who doesn't take easily to compliments but he has, quite simply, been my strength and stay all these years, and I, and his whole family, and this and many other countries, owe him a debt greater than he would ever claim, or we shall ever know." - The Queen's touching tribute in 1997.
"The Duke of Edinburgh has made an invaluable contribution to my life over these past 50 years." - Golden Jubilee speech in June 2002.
:: The Duke on the Queen
"Yak, yak, yak - come on, get a move on." - Shouted from the deck of Britannia in Belize in 1994 to the Queen who was chatting to her hosts on the quayside.
"If you do that once more, I shall put you out of the car." - In the early years of the marriage when the Queen drew breath because she thought Philip was driving too fast.
"Where did you get that hat?" - To the Queen at her Coronation.
"Are you asking me if the Queen is going to die?" - On being asked when the Prince of Wales would succeed to the throne.
"I think the main lesson that we have learnt is that tolerance is the one essential ingredient of any happy marriage. It may not be quite so important when things are going well, but it is absolutely vital when the going gets difficult. You can take it from me that the Queen has the quality of tolerance in abundance." - On their golden wedding anniversary in 1997.
"It's the secret of a happy marriage to have different interests." - At the Royal Windsor Horse Show in 2006.
:: On both
"Together, they are invincible." - The Queen and the Duke's granddaughter Princess Eugenie.
"This was the man with whom Princess Elizabeth had been in love from their first meeting." - King George VI's official biographer Sir John Wheeler-Bennett on Philip.
"Prince Philip is the only man in the world who treats the Queen simply as another human being." - The Queen's former private secretary Lord Charteris.
"He makes her laugh because some of the things he says and does and the way he looks at life is obviously slightly different than her, so together they're a great couple." - Duke of Cambridge on his grandparents in 2012.
"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. And I think he is her rock, really, and she is his." - Eugenie, when Philip fell ill during the Queen's Diamond Jubilee festivities in 2012.
"They get on. They are good together - anyone who knows them well will tell you that." - Philip's late cousin Countess Mountbatten.
"They are different people. Yet they understand one another. Completely. And they are allies." - Author Gyles Brandreth, who examined their relationship in his book Philip & Elizabeth: Portrait Of A Marriage.