Sinn Fein's Martin McGuinness has made a groundbreaking visit to World War One battlefields at Flanders and the Somme.
The self-confessed former IRA chief has paid his respects to the thousands who fell while serving in the British Army.
More than 200,000 Irishmen went to fight in the Great War, and some 49,000 were killed in action.
Soldiers from the north of Ireland (36th Ulster Division) fought alongside those from the south (10th and 16th Irish Divisions).
The 36th Ulster Division and 16th Irish Division had their origins in the Ulster Volunteer Force and Irish Volunteers, the paramilitary forces of the Home Rule crisis.
But those who survived returned to a different Ireland, the war having coincided with the 1916 Easter Rising against British rule.
While the sacrifice of the 36th Ulster Division has been remembered by Ulster unionists, their Irish counterparts were largely forgotten.
Some Irish republicans, including Mr McGuinness' own aide Conor Heaney, have discovered that their own ancestors were British soldiers.
For Mr Heaney the visit to Belgium and France is something of a personal pilgrimage to the grave of his great-grandfather, who fought and died in World War One.
It was not until 1998 that the Island of Ireland Peace Park was established at Messines, Belgium, to honour soldiers from both parts of Ireland.
The Ulster Tower (36th Ulster) at Thiepval and Irish Monument (16th Irish) at Guillemont mark their respective contributions to the Somme.
In that battle alone, the 36th Ulster Division lost 5,500 men and four of its soldiers received the Victoria Cross for their bravery.
Mr McGuinness MLA, now Northern Ireland's Deputy First Minister, said: "World War One is an important part of Ireland's multi-layered history during which tens of thousands of Irish people lost their lives.
"If we are to build understanding and reconciliation on this island, we all need to recognise and accept the complexity of the historical events and different political narratives that make us who we are as a community and as a people.
"I am doing so in a sincere effort to recognise the human suffering and also the importance these events hold for the Unionist section of our people."
Northern Ireland First Minister Arlene Foster MLA and Irish President Michael D Higgins are both expected to attend the official Somme centenary commemoration in July.