His interest was sparked by his uncle Lord Mountbatten, who wrote an official report about an alien in a silver spaceship landing on his estate.
Philip spent last summer reading The Halt Perspective, revealing the inside story of Britain's Rendlesham Forest incident.
Troops at two US airbases in Suffolk witnessed strange bright lights for three nights running from December 26 1980. Officers carried out sorties and one even claimed to have got close enough to touch a triangular spacecraft.
The book was co-written by retired US Air Force Col Charles Halt, who was the base deputy commander at the time, and retired West Midlands detective John Hanson.
In a letter to Mr Hanson, the Duke's private secretary Brigadier Archie Miller-Bakewell wrote: "I am certain it will be read with close interest over the summer."
After receiving another book — Haunted Skies: The Encyclopedia of British UFOs — the Duke's right-hand man replied: "His Royal Highness will add this copy to his collection.
"It will make a most welcome addition to his library."
Last night Mr Hanson said: "Why shouldn't any sensible person have an interest in a phenomena that has baffled mankind for millennia?"
Lord Mountbatten kept his extraterrestrial interests a secret. But after his death in 1979, a report he filed in 1955 was uncovered.
It told how his bricklayer Fred Briggs had a close encounter on his Broadlands estate in Romsey, Hants.
