George Filer, a retired Air Force major, runs the National UFO Center and says it's common to see UFOs around important events.
"The craft seem to have an interest in anything important," Filer told AOL News. "They've been sighted recently over Libya and near the Japanese tsunami."
There are two reasons behind Filer's prediction: In the last few weeks, he's been getting reports from British Royal Air Force pilots who reported seeing UFOs over the English Channel, and, more importantly, he says the royal family is very interested in the UFO phenomenon.
Filer knows this personally because he once had a conversation about UFOs with William's grandfather, Prince Philip.
"It was around 1961 or '62, when I was a navigator in a tanker," Filer said. "He met with a group of us after a dinner because he wanted to talk about UFOs. He told us that the RAF had stopped sending fighters after UFOs because some of them didn't come back.
"They decided to send tankers, which were nearly as fast as the fighters but could hold 15 hours of fuel, compared to two for the fighters."
Filer says the prince also revealed that his interest in UFOs was more than just concerns of national security -- it was personal.
"I asked him why he was so interested in UFOs and he explained that his uncle, the Earl Mountbatten, had seen them up close," Filer said.
Even though the meeting took place during the Cold War, Filer discounts the underlying possibility that the UFOs seen during the period were actually Soviet craft.
"That was always a possibility, but it seemed unlikely since these craft were bigger than expected -- it's like an aircraft carrier in space," he said. "However, the Soviets did try to penetrate the airspace of the United Kingdom and the United States quite regularly."
"The queen even put a book of mine about the subject, called 'Circular Evidence,' on her official summer reading list, the first paranormal book ever included," Andrews told AOL News. "Prince Philip and the queen are particularly interested in the subject. And their interest seems to be based on personal experiences."
Andrews says the queen even sent him a letter confirming that very fact, despite official denials from the British government and the royal family.
"I have numerous documents attesting to that, even though Nick Pope, the head of the UFO project of the Ministry of Defense, publicly stated the queen and the government had no official interest in UFOs," Andrews said. "I believe he was under instruction to make that statement and he later confirmed that during a live interview with the BBC."
Andrews posted the queen's letter on his website but was asked to remove it because it was a "personal" correspondence not meant for public consumption.
"The royal family has not just an interest in UFOs and crop circles, but a great interest," Andrews added. "And that includes Prince Charles and the late Princess Di.
"As for Prince William, I'd be surprised if he wasn't interested as well."
UFO researcher Michael Luckman says Prince Philip's UFO curiosity comes from his uncle, the first Earl of Mountbatten.
"Lord Mountbatten not only had a sighting, but one of his former employees reportedly claimed they saw a craft on [Mountbatten's] estate," Luckman said.
Dan Willis, a Denver genealogist who wrote about Prince Philip in his e-book, "Romanovs in the 20th Century," says that while Mountbatten's sighting was reported extensively in the British press, he wasn't aware of an actual craft -- or that the prince was interested in UFOs himself.
"However, it wouldn't surprise me," Willis told AOL News. "Whatever comes into his mind usually comes out of his mouth, so I can see him talking about this."
UFO sightings is a family tradition, Luckman speculates. He also says Prince Charles was chased by a UFO in 1989 while flying back to Britain from the United States.
Willis says his research shows that the queen has shown interest in crop circles, especially during the 1960s and '70s when they were destroying crops.
"She was even photographed inside a crop circle, but I think her interest was more because this was something that was affecting citizens than her being a real fan," Willis said.
A Buckingham Palace spokesman denied AOL News' interview request on this topic, and Filer isn't surprised.
"Officials at the U.S. government have told me that a head of state will not admit the truth about UFOs unless three or four other heads of state will stand with him," Filer said.
Luckman believes the upcoming royal wedding could be the perfect occasion to make such an announcement.
"I understand if disclosure could be a concern, but if the royal family came through with what they know, it could be a good thing," he said. "I personally feel such an announcement would be a great wedding present to the world."
Although Andrews believes William is just as interested in UFOs as his father and grandfather, he says there is little chance the royal family will make such a disclosure, wedding or not.
"Having knowledge of this phenomenon gives them an edge that can help them maintain power," Andrews said. "Although the royal family has a certain independence that would give credibility to such an announcement, I think if one is made, it is more likely to come through religious sources."
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