Not everyone is enthralled by the prospect of Queen Elizabeth shaking hands with Martin McGuinness today. Since Sinn Fein held itself pointedly aloof from the Queen's historic visit to the Republic last year, there are some sceptical reactions in Dublin, speculating on Sinn Fein's opportunism in now participating in this event.
In London, too, some voices have been raised in dismay: "It is unforgiveable that the Government has put [the Queen] in this position," protested Colonel Graham Dunlop in a letter to the Daily Telegraph. "By agreeing to meet Martin McGuinness, the Queen may be about to make the first real mistake of her reign."
Whatever about Col Dunlop's opinions, he has the situation constitutionally correct: the decision on behalf of the Queen will have been taken by the Government and the Prime Minister, David Cameron.
A British monarch is obliged to do as her prime minister directs, since Parliament is sovereign and has been since the famed Glorious Revolution of 1688.
However, if Elizabeth had strongly objected to the proposed meeting with Mr McGuinness, it is unlikely that Mr Cameron, or the Northern Ireland Secretary, Owen Paterson, would have pressed her.
My own supposition, considering historical precedent, is that Queen Elizabeth was willing to make this demarche, notwithstanding the tragic killing of her cousin, and her husband's uncle, Lord Mountbatten (below), by the IRA in Co Sligo. In his 'home movies' television programme, broadcast over the Jubilee weekend, Prince Charles again wept at the film clip of his great-uncle's funeral.
And, yet, he also said, in the same broadcast, that he thought his mother's visit to the Republic of Ireland last year was one of the great achievements of her reign. We can gather from all this both sadness and regret for the loss of Mountbatten and the way he died and yet a resolution to go forward in peace and reconciliation.
Charles has made this plain, too, in a little-noticed visit that he made to the peace centre at Glendalough in Co Wicklow, in which he spoke of Ireland's sufferings through the centuries, a theme that the Queen also touched on during her Dublin visit - and the wish that "history had been otherwise".
It is sometimes reported that the Queen asks those she meets at Buckingham Palace garden parties, "Have you come far?" Were she to put that question to deputy First Minister McGuinness today, a truthful answer might be: "Yes, very far indeed."
Because it must be fairly acknowledged that Martin McGuinness's journey has been remarkable, from unemployed butcher's boy in Derry, IRA leader and acknowledged tribal chieftain of that rebel hinterland, to accepting the responsibilities of office, winning the respect of Dr Ian Paisley, a trusting working relationship with Peter Robinson and, now, agreeing to a meeting with the monarch.
Every step of the way has been a learning curve and, however much any of us may deplore the atrocities that occurred during the mournful Troubles, we must be glad to see the ballot replace the bullet and those who engaged in violence turn to the responsibilities of political office - and, too, the realities of power.
A united Ireland can never be fashioned from hate and killing: as the late Garret Fitzgerald said, many decades ago: "You cannot bomb a million Protestants into a united Ireland."
But there can be a reconciled Ireland, an Ireland which works together, north and south, through political wisdom and good stewardship.
And surely Peter Robinson and Martin McGuinness have shown an exemplary partnership in working together as they have done.
McGuinness's journey, moreover, clearly began with a reaching-out to the unionist and loyalist community, helped by friendships with Protestant clergy.
There has been true, real progress that is worth celebrating, whatever the difficulties and problems that still occur. And there are still difficulties - not least the continued objections of hardline republicans, who can never accept the monarch's position and describe any encounter with royalty as "fawning".
It will be surely be extraordinary for the Queen today to think back to her Silver Jubilee visit in 1977, which was an unnerving and jittery occasion, when 32,000 troops formed a ring of steel to protect Elizabeth and Philip in Belfast. And the Provisional IRA marched down the Falls Road carrying banners with the words 'ER Queen of Death'. Subsequently, they hanged a mock Queen in effigy.
Black flags mingled with tricolours in nationalist areas. The late Gerry Fitt, normally a conciliator, refused to attend a Hillsborough garden party for the Queen and Prince Philip.
We were still in the period of post-Bloody Sunday. Secretary of State Roy Mason was determined to give no quarter to republicans and, with the exception of the peace leader Mairead Corrigan, Elizabeth met scarcely any nationalists, or Catholics, on that occasion.
The purpose of a modern monarchy is to be a unifying and reconciling force - to bring people from diverse backgrounds together, as George V, Elizabeth's grandfather, was one of the first to understand - and that 1977 Jubilee visit was, in that respect, a notable failure.
The atmosphere is so different for this Diamond Jubilee of 2012 and, in every way, surely, better, warmer, more reconciled, more constructive and more hopeful.
"Have you come far?" Oh, yes, Ma'am, I think we've all come a very long way, indeed.