An agreement to restore power-sharing in Northern Ireland was not the seminal moment.
That came 10 months earlier at the funeral of a journalist shot dead by dissident gunmen in Derry.
Lyra McKee epitomised the ceasefire generation – young people who had grown up in peacetime.
A softly spoken priest publicly rebuked the politicians for their failure to compromise and come together sooner.
“Why in God’s name does it take the death of a 29-year-old woman with her whole life in front of her…”
Father Martin Magill hadn’t even finished his question when applause broke out among the congregation.
A standing ovation, from the back of the cathedral to the front, brought a tidal wave of embarrassment for politicians.
Sinn Fein leader Mary Lou McDonald and DUP leader Arlene Foster were left with little option but to rise to their feet.
“…the death of a 29-year-old woman with her whole life in front of her to get to this point?” he finished.
It was more than a question. It was a pivotal moment, the significance of it immediately palpable for those present.
They included two prime ministers – Theresa May and Leo Varadkar – leaders determined to rescue Stormont.
Within days, Karen Bradley, the then Northern Ireland Secretary, and Irish Foreign Affairs Minister Simon Coveney convened negotiations.
But there were too many obstacles – the DUP were wielding influence in Westminster and had less reason to compromise at home.
Brexit talks were straining relations between London and Dublin, not to mention between the two former devolution partners: the DUP and Sinn Fein.
The clerical rebuke had provided the key; but it took an electoral rebuke – both parties hammered in a general election – to open the door to compromise.
Prime Minister Boris Johnson no longer needed the Democratic Unionists and had the majority to secure a Brexit deal.
Mr Coveney and Northern Ireland Secretary Julian Smith seized their opportunity to negotiate a new power-sharing agreement.
By conceding that the greater good did not require a winner and a loser, the DUP and Sinn Fein had answered Father Magill’s question.
There is no reason why the two parties could not have come together sooner and closed the political vacuum filled by gunmen.
But that seminal moment during her funeral has ultimately led to a pivotal point on the long path to peace in Northern Ireland.
When Arlene Foster and Sinn Fein deputy leader Michelle O’Neill are sworn in as First and Deputy First Ministers, many will be thinking of Lyra.
Months after her untimely and unnecessary death, the hope she had come to epitomise lives on in the words she left behind.
Mr Coveney borrowed some of them when breaking the news of a potential agreement at Stormont.
“Northern Ireland is a beautiful tragedy, strangled by the chains of its past.
“It’s a place full of darkness and mysteries. It’s also my home.”
Thank you Lyra. Rest in peace.
Senior Ireland correspondent @skydavidblevins An agreement to restore power-sharing in Northern Ireland was not the seminal moment. That came 10 months earlier at the funeral of a journalist shot dead by dissident gunmen in Derry. Lyra McKee epitomised the ceasefire generation – young people who had grown up in peacetime.