Britain's Queen Elizabeth, Prince Philip, and Prince William
Britain's Queen Elizabeth (C), Prince Philip (R), and Prince William, walk amongst spring blossom and flowers as they arrive to attend the unveiling of the Windsor Greys statue in Windsor southern England March 31, 2014. The statue marks sixty years of Queen Elizabeth's Coronation in 2013 and the important role played by Windsor Greys in the ceremonial life of Britain's royal family. Reuters/Toby Melville

Four young Islamic terrorists planned to assassinate Queen Elizabeth by stabbing her at the Royal British Legion Festival, a military party held in Royal Albert Hall. The event is scheduled on Saturday, Nov 8.

The Sun reports that the four extremists, aged 19 to 27, were arrested by British police on Thursday night. Besides a knife, the police found in their possession firearms. They were arrested on suspicions of committing, preparing or instigating acts of terrorism, according to the Metropolitan police.

Authorities informed the 88-year-old Queen about the assassination plot, but despite the threat to her life, she and Prime Minister David Cameron would still attend to her royal duties this weekend such as wreath-laying rites at the Sunday Remembrance celebration to mark the end of World War I in 1918.

Besides the Queen, other members of the British royal family would attend the events as well as political and military leaders. The event's finale would be a two-minute silence while poppy petals fall from the roof to represent Britons who died in World War I.

Britain raised in August the national terror threat to "severe" from "substantial" because of the "highly likely" chances of a terrorist attack. The heightened alert is linked to possible retaliation by Islamic State extremist over the UK air strikes in the Middle East.

There had been previous attempts to assassinate the Queen that were foiled.

On June 13, 1981, 17-year-old Marcus Serjeant fired six shots at the monarch while she was riding her horse Burmese for her Birthday Parade. But after police subdued the teen, they discovered he only fired blank shots. He planned to get hold of a live firearms and kill the Queen because he wanted to be famous, but he failed.

There was another one in the 1970s while the Queen and Prince Phillip were in Australia.

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