The son of the exiled Prince Andrew of Greece, Philip married the queen in 1947 and is now the longest-serving consort and oldest-serving spouse of any British monarch.
Britain's Prince Philip, renowned for his blunt talk and verbal gaffes, turns 90 on Friday, spending the day as he has much of life performing official duties in his role as Queen Elizabeth's husband.
The son of the exiled Prince Andrew of Greece, Philip married the queen in 1947 and is now the longest-serving consort and oldest-serving spouse of any British monarch.
Despite being a near constant companion at the queen's side during her long reign, the still sprightly prince has rarely sought the limelight himself.
His birthday will be in keeping with that low-key style; he will hold a reception to mark the centenary of a charity for the deaf and in the evening he will chair a conference for senior British military figures followed by a dinner.
"It's a normal working day for him. There's no celebration as such," his spokesperson said.
The only formal event to mark his birthday will take place on Sunday with a special service at St George's Chapel in Windsor Castle, one of the queen's residences, west of London, which will be attended by most of the royal family.
Philip, the oldest living great-great-grandchild of Britain's Queen Victoria, was born Prince Philip of Greece and Denmark on the Greek island of Corfu in 1921.
His family was forced into exile when Philip was 18 months old and he came to England as a child, later becoming a naturalised British citizen.
He served in the Royal Navy during World War Two, taking part in the Allied landings in Sicily and was in Tokyo Bay when the Japanese surrendered in 1945.
He first met his future wife when she was 13 and visited the naval college where he was a cadet, and following the war they got engaged, when he was given the title the Duke of Edinburgh.
As the queen's husband he has no clear constitutional role, although he does accompany his wife on most of her official engagements in Britain and all her foreign trips.
"He has, quite simply, been my strength and stay all these years," the queen said in a personal tribute to Philip during a speech to mark their 50th wedding anniversary in 1997.
"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."
His most notable achievement is the Duke of Edinburgh Award scheme for young people, which is estimated to have attracted about seven million participants from 132 countries since 1956.
"This is an inspiration," British Prime Minister David Cameron told Parliament on Wednesday. "His is a huge achievement for which this country and many others owe the duke a deserved debt of gratitude."
However, he still probably remains best-known for gruff and unguarded remarks and gaffes, with his sayings even being published in several books.
He once told British students in China: "If you stay here much longer, you'll be slitty-eyed" and asked Aborigines in Australia if they still threw spears at each other.
Cameron said Philip had always done things "in his own inimitable way, with a down-to-earth, no-nonsense approach that the British people I believe find endearing".
While Philip has spent his life in the shadow of the queen, there is one place where he outshines his wife -- on the south Pacific island of Tanna in the Vanuatu group, where the locals worship him as a god.
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