The word "young" leaps out from the title of Philip Eade's book. Prince Philip, whose 90th birthday was yesterday, has been a grumpy old man for longer than most of us can remember. A young Philip is as unimaginable  almost  as a teenage Gandhi. (Almost as unimaginable was the venerable Gandhi's royal wedding gift in 1947: Mahatma's handspun tray-cloth was loyally defended by a youthful Philip when his fiancée's granny, mistaking the scrap of material for the Indian leader's loin-cloth, cried out, aghast, against "the horrible thing!")

Eade's staunchly unhagiographic book is well spiced with such royal titbits, and enlivened by a lemony tartness in the author's tone. Citing press speculation about the likelihood that Philip's Nazi brother-in-law would be excluded from the royal wedding, Eade observes that Prince Christoph of Hesse-Cassel was indeed an unlikely invitee, "if only because he had died three years earlier".

The decision to focus on Philip's early life was well taken: who needs to be reminded of all those commonwealth tours or  often during those same interminable junkets  of the duke's devastating gaffes? Eade's story of Philip's family history, while rich in drama and tragedy, helps to source the Duke's stubborn bloody-mindedness, if not his uncommonly forthright views, in a bizarre upbringing.

The youngest child, by seven years, in a brood of handsome girls, Philip was born in 1921 (on a dining-room table in Corfu) to a half-Danish father (Prince Andrea of Greece) and a completely deaf German mother. (Princess Alice hid the defect well; she became a proficient lip-reader in several languages.) In 1922  following the siege of Smyrna and a coup by Greek revolutionaries  Andrea's older brother was forcefully encouraged to abdicate from the throne of Greece. Prince Andrea himself, sentenced to death by an Athenian court, was saved only by British intervention (he was a first cousin of George V). Aged 18 months, Philip travelled with his parents into exile. The improbable story that his shipboard cradle was a fruit crate is, according to Eade's researches, true.

Life did not become easier as an outcast. Housed in Paris by Andrea's peculiar brother, "Big George", and his fascinating, promiscuous wife, Marie Bonaparte, the banished family quickly fell apart. Philip's father, a handsome giant, left for a new life with a mistress in the South of France; Philip's mother, following a breakdown in 1929, turned recluse. (Inspired by the example of a saintly German aunt, Alice eventually became a nun.) Her quartet of daughters, by 1932, had all married German princes. And as for Philip, the flax-haired child attendant at all these foreign weddings to strangers: "I just had to get on with it. You do. One does."

In 1946, touting his nephew's qualifications as a suitable husband for Princess Elizabeth, the manipulative and supremely bossy Lord Mountbatten pronounced Philip to be a young man "more English in nationality than anything else". Certainly, from the age of nine, he had experienced an English upbringing. Living at Lynden Manor, Berkshire, with his Aunt Nada and  yet another  Uncle George (Mountbatten's clever and much nicer older brother), Philip attended English prep school, acquired an enduring faith in Spartan discipline, and  according to one American film actress visiting Lynden in 1935  enjoyed such teenage pranks as making apple-pie beds.

Certain of Philip's virtues and foibles were already becoming apparent. Praised at school for his outstanding sense of service, he was also characterised as impulsive, irritable and rude. Sailors serving under Philip's command in the Navy would later draw similar conclusions.

Philip had just started naval training in 1939 when he met Elizabeth. She, according to her garrulous nanny, was smitten. Left to himself, as Eade makes clear, Philip would happily have dispensed with the matchmaking energies of his dear uncle "Dickie". Mountbatten was warned, in one letter, that Philip felt himself coerced into wooing "by proxy". Elizabeth's young suitor was being naïve.

Mountbatten's contribution, an important one, was to muzzle a fiercely German-averse British press. Come the wedding day, in November 1947, even this newspaper (not known for its love of the monarchy as an institution) offered few criticisms.

Eade's account is as thoughtful and unbiased an explanation as we are likely to get of the contentious, sensitive, grouchy old martinet who, for all his flirtations, has proven himself a loyal consort to the queen. And one whose singular interest in UFOs  an intriguing sideline in Eade's book  suggests that he may share more in common with Prince Charles than most of us imagine.)

Miranda Seymour's Chaplin's Girl is published by Pocket Books.

 This article was amended on 15 June 2011. The original said Lynden Manor is in Kent. This has been corrected.