LONDON — On a national tour of sorrow, King Charles III has heard many expressions of condolence for the death of his mother, Queen Elizabeth II. But few were as tinged with symbolism as the one delivered on Tuesday by the speaker of the Northern Ireland Assembly, Alex Maskey, at a royal castle outside Belfast.
Mr. Maskey is a member of Sinn Fein, the Irish nationalist party, which is now the largest in the territory. He was once jailed for his involvement with the Irish Republican Army. It’s a sign of how much has changed that Charles, whose great-uncle Louis Mountbatten was assassinated by the I.R.A. in 1979, smiled sadly when Mr. Maskey switched to Irish to say, “May she rest in peace.”
Charles and his mother each played a role in trying to reconcile the Irish and British after the blood-dimmed tide of the Troubles. The fruits of their efforts were on vivid display in a bereaved Belfast. Yet the new king also confronted a Northern Ireland that is drifting inexorably, if slowly, toward the Irish Republic — another part of the United Kingdom that could slip away during his reign.
“The death of the queen comes at a moment when unionism in Northern Ireland is feeling particularly anxious and uncertain about the future,” said Katy Hayward, a professor of politics at Queen’s University, Belfast.
“But it also puts nationalist leaders in a difficult position,” Professor Hayward said. “Many nationalists feel uncomfortable with the king. At the same time, they’ve got to be considerate of other people who feel differently.”
The unionists, who want to stay part of the United Kingdom, are fearful that post-Brexit trade rules, known as the Northern Ireland protocol, will erode their ties to Britain, hastening the day when the territory’s growing nationalist, predominantly Roman Catholic population will vote to leave and unify with Ireland.
Under pressure from the unionists, Britain’s prime minister, Liz Truss, has threatened to scrap the trade rules, provoking tensions with the European Union and Ireland that some fear could erupt into a full-blown trade war.
Still, Northern Ireland’s fraught politics took a back seat on Tuesday to a day of rituals and mourning for the queen, which spoke to her appeal on both sides of the Irish border. Her visit to the Irish Republic in 2011 — during which she wore green, expressed regret for Britain’s painful history with Ireland and tried out some Irish — is remembered there as an electric moment of personal diplomacy.
Mr. Maskey praised the queen for recognizing the power of a small gesture to bridge bitter gaps between people. Elizabeth, he said, understood that “one tradition is not diminished by reaching out to show respect to another.”
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Charles replied that the queen “never ceased to pray for the best of times for this place and its people, whose stories she knew, whose sorrow our family had felt and for whom she had great affection and regard.” She saw her role, he said, as someone who could try to bring together “those who history had separated.”
The new king pledged to continue that work. Having made 19 trips to Northern Ireland with his wife, Camilla, he can claim a credible record as a diplomat. He has also reached out to Ireland, despite the blow of Lord Mountbatten’s killing, which deprived him of a beloved mentor.
In 2010, Charles attended a gala party in his honor at the Irish Embassy in London, where he mingled with guests like the singer Bob Geldof, was serenaded with Irish music and was toasted by a famously peppery Irish radio personality, Terry Wogan, who thanked him, tongue in cheek, for “800 years of oppression.”
Bobby McDonagh, the former Irish ambassador to London, who played host at the party, said Charles had been thrilled by the reception. Mr. McDonagh recalled his pointing out that the embassy was across the road from the garden at Buckingham Palace, where he had played as a child. If Charles had known that at the time, he told his host, he would have thrown pebbles at the embassy’s windows.
In 2015, during a visit to Ireland, Charles played his own part in reconciliation by shaking hands with Gerry Adams, who was then the leader of Sinn Fein, the political wing of the underground I.R.A. Mr. Adams had long described Lord Mountbatten, who had once led Britain’s armed forces and had a vacation home in Ireland, as a legitimate target in the I.R.A.’s armed struggle against the British government.
Mr. Adams did not apologize for the killing during that encounter. But last year, on the day after the queen’s husband, Prince Philip, was buried, the current leader of Sinn Fein, Mary Lou McDonald, issued a landmark apology. “Of course, I am sorry that happened,” she told a London radio station. “Of course, that is heartbreaking.”
On Tuesday in Belfast, King Charles greeted the president of Ireland, Michael D. Higgins, who attended a memorial service for the queen. That made him the first head of state to meet the king since his accession to the throne.
He also took note of the new political landscape in a brief exchange with the leader of Sinn Fein in Northern Ireland, Michelle O’Neill. As the head of the largest party, she has been designated as the first minister in the territory’s power-sharing government. But the unionists have refused to take part in it, citing Britain’s impasse with Brussels over the trade rules.
“What are you now, the biggest party are you?” the king asked Ms. O’Neill.
She replied, “We are, indeed.”
“All that skill and ingenuity,” Charles said with a smile.
Mr. Maskey, the assembly speaker, gestured to the nearby figure of Jeffrey M. Donaldson, the leader of the Democratic Unionist Party, which once held that status. “Don’t be telling Jeffrey that now,” he said.
Ms. O’Neill has struck a conciliatory note, saying last week that the queen nourished ties with “those of us who are Irish, and who share a different political allegiance and aspirations to herself and her government.”
Unionists relished the display of royal pomp, saying they were grateful that Charles had visited so quickly. For now, “the protocol is not in our minds,” said David Campbell, chairman of the Loyalist Communities Council, which represents a group of pro-union paramilitary groups that vehemently oppose the trade rules.
Still, some scholars questioned whether, over the long term, the unionist population would find the king as reassuring a figure as his mother. Many of them particularly identified with the queen’s religious faith, Professor Hayward said.
Charles comes across as a less conservative figure, embracing interfaith communication and issues like climate change. That does not appeal to the deeply conservative Democratic Unionists, Professor Hayward said. He is also divorced, she noted, which rankles some older unionists.
In unionist and loyalist strongholds in Belfast and Derry, the queen’s image is ubiquitous in store windows and on murals. Images of Charles are fewer. The English king who features prominently in unionist iconography is William of Orange, who won a famous military victory over a Catholic king, James II, in 1690.
Most experts said they doubted the transition from Elizabeth to Charles would alter the political dynamic in Northern Ireland, which is rooted in causes that stretch back much further than the dawn of her reign.
“I would expect Charles to perform fairly well as king,” said Mr. McDonagh, the former Irish ambassador to London. “But regardless of how he performs, I wouldn’t expect it to diminish one bit the unionists’ desire to remain in the union. I also don’t think it will change the aspirations of the nationalists.”
