Prince Charles and the Duchess of Cornwall reviewing the troops in Dublin to celebrate the centenary of the 1916 Rising? That will be a 'pinch yourself' moment.
Until recently it would have sounded more like the absurd backdrop for an alien invasion in the next series of Dr Who than something that was actually in prospect. Now it's a subject for polite table talk at State banquets in Windsor Castle.
The Queen herself mentioned it when she said that her family hopes to "stand beside" those commemorating the centenaries of events leading to the Irish Free State's creation.
The details are now being worked out and journalists are being briefed in Dublin to accustom the public to the idea.
Predictably, there are a few jitters. Tom Elliott, the UUP MLA for Fermanagh and South Tyrone, described the idea as "inappropriate", adding: "I think it could be seen as an acceptance and acknowledgement that terrorism is okay."
That can be avoided. Instead, it presents an opportunity to consign the physical force tradition in Irish politics to the history books; to acknowledge its role and move on.
It can help reset British/Irish and north/south relations. The DUP is already talking in terms of how it should be handled, not whether it should happen.
"The British Government has already indicated that a member of the royal family will take part in the centenary," said Jeffrey Donaldson. He added that "there are very real sensitivities around this anniversary, because there were British soldiers who were killed during the Easter Rising and it is important that they are remembered".
No doubt they will be. Yet most casualties were civilians caught up in the fighting, or the artillery fire, as much of the centre of Dublin was destroyed.
Some 116 British soldiers and 16 Royal Irish Constabulary members died. In all, 64 insurgents were killed in action; 254 civilians died – 40 of them children. Both sides shot civilians who did not stop at checkpoints.
It is the same in all our conflicts. The Cain archive, maintained by the University of Ulster, records that 1,841 of the 3,531 people killed in the Troubles were civilians.
'Never again', is the predominant lesson of such conflicts. Whatever the rights and wrongs of old struggles, we now have a democratic means of settling political differences and there is no excuse for any new resort to violence.
Martin McGuinness made this clear when he said, during his 2011 Irish presidential campaign, that there is only one Oglaigh na hEireann (Army of Ireland, traditionally the Irish name for the IRA) and that is the army of the Irish state. Only last weekend Peter Robinson made it clear that maintaining the Union was now a matter of winning political arguments.
Good relations between the Irish Republic and Britain, cemented by unmistakable gestures like those planned for 2016, can help our parties keep on-track, but they did not happen by accident.
One important player is Co-operation Ireland, the peace-building charity, whose patrons are the Queen and Irish President Michael D Higgins.
It hosted the first historic handshake between the Queen and Martin McGuinness at a reception that was also attended by Peter Robinson and President Higgins in the Lyric Theatre in June 2012. It was also consulted on the two State visits and has been active in peace-building on the ground.
Christopher Moran, the organisation's chair, believes that "most people are more interested in our shared present and our shared future, rather than our shared past".
Coming to terms with the past – not forgetting its lessons, or refighting its quarrels – is an essential part of that process.