Queen Elizabeth.Photo:Tim Graham Photo Library via Getty

Tim Graham Photo Library via Getty
The FBI was aware of frightening threats againstQueen Elizabethduring her tour of California 40 years ago.
Queen Elizabeth, Prince Philip, President Ronald Reagan and Nancy Reagan.David Levenson/Getty

David Levenson/Getty
Queen Elizabeth.David Cairns/Getty

David Cairns/Getty
President Ronald Reagan and Queen Elizabeth.Tim Graham Photo Library via Getty

The files added that authorities planned to contact the patron, “who has been interviewed in PIRA cases and has been generally cooperative, although he makes no secret of his sympathies for the IRA.”
The royal visit to the U.S. came during the Troubles, the 30-year conflict in Northern Ireland that divided unionists and nationalists over whether Northern Ireland should stay within the U.K. or join the Republic of Ireland, theBBCreported. Groups from both sides like the IRA and Ulster Volunteer Force carried out attacks, and British troops were deployed to Northern Ireland.
Queen Elizabeth.Anwar Hussein/Getty

Anwar Hussein/Getty
Can’t get enough of PEOPLE’s Royals coverage?Sign up for our free Royals newsletterto get the latest updates on Kate Middleton, Meghan Markle and more!
Despite the threat, the FBI reported that Queen Elizabeth’s visit to California wrapped “without incident,” and the case was closed.
Elsewhere in the extensive file, before the Queen visited Kentucky in 1989, the FBI noted that “the possibility of threats against the British monarchy is everpresent from the Irish Republican Army.” Two years later, in 1991, the federal law enforcement agency was on alert for protests when she attended a Baltimore Orioles game with President George H.W. Bush.
source: people.com