The Queen will meet a former senior commander of the IRA today, 33 years after the organisation murdered her cousin.
The meeting with Sinn Fein's Martin McGuinness, now Northern Ireland's Deputy First Minister, is regarded as a defining moment in Anglo-Irish history.
The meeting and handshake will take place on what could best be described as neutral territory. The cultural event, at Belfast's Lyric Theatre, is organised by Co-operation Ireland, a cross border group, and the event will also be attended by Irish President Michael D Higgins.
It is still not certain whether cameras will be allowed to cover the meeting in full or whether there will be restrictions on pictures and audio.
Although, as Head of the Commonwealth, the Queen has met many men who once fought against British rule, what makes this encounter so poignant is the IRA's assassination of Lord Louis Mountbatten in 1979.
Mountbatten, the last Viceroy of India and an uncle of Prince Philip was killed when his boat was blown up in Mullaghmore, in the Irish Republic.
Three other passengers died, including his 14-year-old grandson Nicholas and a 15-year-old local boy, Paul Maxwell, who was helping on the boat.
Rodney Lomax should have been on board as well. He was responsible for maintaining the 27ft boat Shadow V, and the Earl had asked him to come on the trip to fix a problem. But he declined because he was going on holiday. He was on shore when he heard the explosion.
"It was awful for everybody, because nobody here would have anything to do with a thing like that," Mr Lomax said.
He told Sky News that he welcomed the handshake as a moment of reconciliation. "I'm not in the IRA and never was, but I'm republican-minded and I think it's great," he said.
Local historian Joe McGowan was also in Mullaghmore when the blast happened. He told Sky News that both the monarch and the former IRA commander have "stepped up to the plate" to achieve reconciliation.
"From the Queen's point of view she lost a member of the family, so it's a big step for her," Mr McGowan said.
"Martin McGuinness is conceding something. He has to recognise that the struggle over the past 30 years was lost, in a military sense anyway."
The man who planted the bomb, Thomas McMahon, was jailed for life, but like other prisoners, he was freed in 1998 as part of the Good Friday Agreement which ended the IRA's military campaign.
He now lives in County Monaghan, but declined to talk to Sky News about the bombing, or the Queen's visit.