Not so long ago, the image would have been unimaginable: the Queen shaking hands with a man who was an Irish Republican Army commander when the infamous group murdered her husband's favourite uncle, Lord Mountbatten in 1979.

Now, though, the meeting today between Elizabeth and Martin McGuinness, Sinn Fein's deputy prime minister in Northern Ireland, has become the most high-profile symbol of a long-sought reconciliation between Catholics and Protestants in that troubled part of the world.

"When they shake hands, there's almost a kind of peace between the opposing forces who were noted for their outrageous behaviour over the past 25 years or more," says Ninian Mellamphy, a professor emeritus at Western University in London, Ont., who came to Canada from his native Republic of Ireland five decades ago.

Sinn Fein's Martin McGuinness waves to the media at Dublin Castle, Ireland, on Oct. 28, 2011. (Petet Morrison/Associated Press)

Mellamphy, a long-time royal watcher, sees much symbolism in the meeting at a charity reception in Belfast.

"She is symbolically the head of the British forces who committed some terrible outrages in the north of Ireland and he, as one of the leaders of the IRA and now a leader of Sinn Fein, was also responsible for, in a symbolic way or maybe in an actual way, for all sorts of outrages ... by the IRA."

Yet somehow, even with the bombing murder of Lord Mountbatten of Burma in a boat off the Irish coast near Sligo in 1979, all that seems to be behind them.

"In a sense, each of them is more or less acknowledging the past and perhaps cementing a future," says Mellamphy.

"It will be like a treaty, a reconciliation, he representing the republican movement and what it has done in history and she representing the unionist movement and its particular place in history."

Bloody conflict

It is a troubled history.

More than 3,600 people on both sides of the Northern Ireland conflict were killed since 1969. The Troubles, as they came to be called, cast a pall over life in Britain and Ireland for decades.

British military families wouldn't leave home without checking to make sure there wasn't a bomb under the car. Cautious grandparents would urge against a shopping trip to central London, which was the target of IRA bombs over the years. And so on.

One date became a particular touchstone (and even the title of a U2 song): Bloody Sunday, Jan. 30, 1972, when British paratroopers fired on a crowd in Londonderry, also known as Derry. The gunfire killed 13 unarmed Catholic men. Fifteen more people were wounded.

Twenty-eight years later, following a 12-year inquiry into the event, British Prime Minister David Cameron said the soldiers' actions on that day were unjustified.

Against the violence was a widespread desire to make it disappear.

The most significant milestone — apart from Wednesday's handshake — was arguably the Good Friday Agreement of 1998, a landmark accord because of a clause that called for "the decommissioning of illegally held arms in the possession of paramilitary groups."

The peace process remained a difficult one, however, with the IRA's failure to disarm immediately a key stumbling block.

In 2005, the IRA announced an end to its armed struggle to end British rule in Northern Ireland. The paramilitary organization instructed its units to dump its arms and for its volunteers to "assist the development of purely political and democratic programs through exclusively peaceful means."

Almost two years later, an agreement to share power between Protestants and Catholics was announced between the two hardliners of Northern Irish politics, Gerry Adams of Sinn Fein and Ian Paisley of the Democratic Unionist Party.

Willing to talk

Mellamphy was in Ireland in 2007, and he remembers seeing a picture of Paisley, the Northern Ireland first minister, with McGuinness, who was the deputy first minister in the power-sharing government.

"You'd swear to God that they were uncle and nephew with McGuinness with his hand gently on the back of Ian Paisley ushering him through a door," Mellamphy says. "I thought, my God, neither of them would ever have exchanged a word 10 years before."

Northern Ireland's Deputy First Minister Martin McGuinness, front left, and First Minister Ian Paisley, back left, leave Stormont Parliament Buildings in Belfast, with Irish Prime Minister Bertie Ahern, front right, and British Prime Minister Tony Blair on May 8, 2007. (Peter Morrison/Associated Press)

In that meeting he sees a precursor to Wednesday's handshake in Belfast.

"In a strange way, the handshaking with the Queen is a much easier image to expect than, let's say, the kind of almost fraternal or familial relationship between McGuinness, who belonged to one extreme, and Ian Paisley, who belonged to the other."

A successful visit by the Queen to the Republic of Ireland last year also helped lay the groundwork for Wednesday's meeting.

Sinn Fein refused to participate in that Royal Visit, a decision the Irish Independent said in an editorial this week "struck even those of a nationalist bent as churlish."

Politics in peace

This time around, Sinn Fein has no such apparent hesitation.

Leader Gerry Adams told the BBC the decision to accept an invitation for McGuinness to meet the Queen is a "very significant step."

"It's good in terms of national reconciliation, it's good in terms of conflict resolution, and while there are still elements here who don't engage in talks and stand back from embracing the peace process, I think it perhaps opens the door to them also."

Others see a more crass politics at work in Sinn Fein's actions.

"The strategic thinking behind [the] meeting is consistent with Sinn Fein's expansionist strategy in the south of Ireland," Anthony McIntryre wrote in the Guardian Tuesday. "Its electoral ambitions, not reconciliation with unionism, are what fuels McGuinness's meeting the Queen."

"However," he went on, "having scorned the opportunity during the Royal Visit to Ireland last year, Sinn Fein's transparently crass manipulation of tomorrow's event may end up alienating more votes than it attracts."

In Ireland, it seems, total peace of any kind will always be at least a little bit elusive, no matter who shakes hands with whom.

With files from CBC News