FBI documents revealed that Queen Elizabeth II was under threat of assassination during a visit she made to the US in 1983.
The documents, which are about the late queen's visit to the US, reveal that the FBI, which took part in her security, feared threats from the Irish Republic Army (IRA).
According to the documents, on February 4, 1983, about a month before the queen visited San Francisco, a local police officer alerted federal agents of a potential threat to her. The same police officer, who frequented a pub in the city, got a phone call from a man he met in the pub who told him that he was determined to avenge the death of his daughter who was killed in Northern Ireland by a rubber bullet.
According to the police officer, the man "would try to harm Queen Elizabeth by dropping an object from the Golden Gate Bridge onto the Royal Britannia yacht while it was sailing under the bridge or would try to murder the queen while she was visiting the Yosemite national park."
After hearing about the threats, the Secret Service planned to block all the roads leading to the bridge while the yacht was passing under it.
It's unclear what security measures the Secret Service took for the queen's visit to Yosemite, but the visit was made without incident.
Documents show FBI was always wary of threats to the queen
A database of 102 pages of FBI documents about Queen Elizabeth II's visits to the US was publicized this week in response to a "Freedom of Information" law request filed by NBC News.
The documents also revealed that FBI agents regularly shared intelligence with the Secret Service and local police stations regarding the IRA and its supporters leading up to the queen's visits to the country.
The American fear of possible harm to the royal family while visiting the US was not taken lightly. In another incident in 1989, before the queen's visit to the East Coast, an internal FBI memo stated that despite a lack of intelligence reports on specific threats, "Boston and New York are being asked to prepare for any threat against Queen Elizabeth II by IRA members."