The pictures of former IRA commander Martin McGuinness shaking hands with the Queen were viewed around the world as an iconic mark of progress.
Taken at an arts event in Belfast in 2012, the two former adversaries briefly came together in mutual respect.
Former US secretary of state Hillary Clinton described the event as "the most remarkable sign of change yet" in the Northern Ireland peace process.
For years, McGuinness played a significant role in the Provisional IRA, overseeing bombing campaigns and attacks on British troops and civilians.
He has been described as “one of the most dangerous enemies the British state ever had”, though he later became Deputy First Minister of Northern Ireland.
Conversely, the Queen is the head of the British state and armed forces. She also lost her cousin, Louis Mountbatten, to an IRA bomb in 1979 – when McGuinness was the organisation’s chief of staff.
Therefore, the meeting between the two was seen as a clear demonstration of reconciliation in Northern Ireland.
Its significance was not lost on the only photographer to record the event, Paul Faith of the Press Association.
"I feel so privileged to have witnessed that significant and historic moment," Mr Faith said.
He added: "I remember that Martin appeared very relaxed and confident and happy to stand beside the Queen.
"The significance of it for me didn't really sink in until the next day when I saw the pictures in the papers.
"Every front page was carrying the photograph and it hit me that this was going to be a historic image."
The day after shaking hands with the Queen, McGuinness spoke about its "momentous and historical" significance.
He said that the meeting had the potential to define "a new relationship between Britain and Ireland and between the Irish people themselves".
In a speech in Westminster he said the handshake "was in a very pointed, deliberate and symbolic way offering the hand of friendship to unionists through the person of Queen Elizabeth for which many unionists have a deep affinity".
"It is an offer I hope many will accept in the same spirit it was offered," he said.
A few years later McGuinness paid tribute to the Queen for meeting him.
"I liked her courage in agreeing to meet with me, I liked the engagements that I've had with her. There's nothing I have seen in my engagements with her that this is someone I should dislike - I like her," he told a BBC documentary.
Additional reporting by Press Association.