Queen Elizabeth has said that the 1982 Hyde Park IRA bombing was “the most ghastly” of her life.

On July 20, 1982, members of the IRA detonated a car bomb on South Carriage Drive which killed four soldiers and seven horses as they rode through Hyde Park during the Changing of the Guard procession.

Read More: What Queen Elizabeth thought meeting ex-IRA leader Martin McGuinness

Brigadier Andrew Parker-Bowles, the former guardsman and ex-husband of the Duchess of Cornwall, was leading the Queen’s Calvary that day and described the mount in Rober Hardman’s book, "Queen of the World."

He told Hardman: “One of the barriers opened and someone said, ‘They've blown up the Guard.’ So we ran down to where the smoke was rising.

“The first horse I saw was Sefton. He had a bloody great hole in him but he managed to pull through.”

Afterward, Parker Bowles had the opportunity to speak to the Queen.

“She said to me it was ‘The most ghastly day of my life.’”

Read More: Queen Elizabeth is a descendant of Irish High King Brian Boru

The explosion killed Roy Bright, Dennis Daly, Simon Tipper and Jeffrey Young. Other members of the Royal Household Cavalry were also injured. In total, some 31 people were injured. Seven horses were also killed.

The prime suspect in the bombing, John Downey, avoided prosecution due to an error made by British police, who sent a “letter of assurance” to Downey in 2007 stating he was not wanted for the attack despite there being an outstanding warrant against him.