She was making the same gesture of forgiveness for her family.
Though the conflict between Ireland and Great Britain goes back centuries and has claimed some 3,700 lives in just the last four decades, one of its high-profile victims was a member of the queen's own family.
In 1979, Lord Louis Mountbatten, the last viceroy of India, was killed by a bomb planted in his yacht, the Shadow V, anchored in the waters off the Irish Republic's County Sligo. The Irish Republican Army took responsibility for the bombing and, experts say McGuinness, 62, was the IRA's chief of staff at the time.
A British statesman and naval officer, Mountbatten was an uncle to the queen's husband, Prince Philip, Duke of Edinbugh, and a second cousin to the queen. It was Mountbatten who introduced the 13-year-old Princess Elizabeth to Prince Philip of Greece, then a cadet at Dartmouth Royal Naval College, in the summer of 1939. Eight years later, the two were married.
Mountbattan also had a role as godfather and mentor to their oldest son, Prince Charles, Prince of Wales, who biographers say, was devastated by the assassination.
The prince drew on that experience when he spoke to relatives of the 9/11 victims at a service on the attack's 10th anniversary at the memorial Gardens in Grosvenor Square.
Referring to the 1979 murder of his "greatly loved great uncle" Lord Mountbatten, Prince Charles said, "At the time I remember feeling intense anger, even hatred of those who could even contemplate doing such a thing. But then I began to reflect that all the greatest wisdom that has come down to us over the ages speaks of the overriding need to break the law of cause and effect and somehow to find the strength to search for a more positive way of overcoming the evil in men's hearts."