Prince Philip investigated UFOs for 70 years, it has been claimed.
Alien buffs have called for ministers to make the late Duke of Edinburgh's findings public following the death of his wife Queen Elizabeth.
Prince Philip, who died aged 99 in 2021, developed a "fascination" for little green men after a close encounter at the home of his uncle Lord Louis Mountbatten in 1955.
It has been claimed that the late royal spent much of his life investigating extra-terrestrials but the matter was kept quiet as it would have "caused a sensation".
Former Ministry of Defence official Nick Pope, who manned the UK Government's UFO research during the 1990s, claimed that Philip - who was the husband of Queen Elizabeth II, who passed away in September aged 96 - "kept an eye on developments, subscribed to UFO magazines and newsletters and had witnesses interviewed".
Speaking to History TV in America, Pope said: "This is highly sensitive.
"Here you have the Queen's husband investigating UFOs. Had the news got out it would have caused a sensation."
Historian Richard Dolan has also claimed that Lord Mountbatten “talked extensively to Prince Philip about this” his UFO experience, adding: "You have to assume Queen Elizabeth knew.’’