Census figures outlining the religious make-up and sense of national identity of people in Northern Ireland were published on Thursday.
For the first time in its 101-year history, the figures show that more people in Northern Ireland are Catholic than Protestant.
This is a day Northern Ireland's unionist founders were confident would never happen. It will unnerve many unionists and loyalists.
When Northern Ireland was created in 1921, it was designed to have an inbuilt unionist majority.
In April 1934, former Northern Ireland prime minister and Ulster Unionist leader James Craig described Stormont as "a Protestant parliament for a Protestant state", contrasting it with what he described as "a Catholic state" in the Republic.
What many historians have called the demographic clock has been inevitably ticking towards this moment in recent decades.
Put simply, the Protestant population is older and has a higher mortality rate, while the Catholic population is younger.
It isn't just the number and proportion of people who define themselves as Catholic that has increased, so too has the number describing themselves as "Irish only" in terms of national identity.
In contrast, the number describing themselves as "British only" has decreased along with the proportion of Protestants.
Unionists will point to those figures on identity as evidence that if this trend continues and Catholics at some point become more than 50% of the population, that does not automatically translate to majority support for a United Ireland.
While 45.7% of Northern Ireland's population is Catholic, just over 29% of the overall population define themselves as "Irish only".
But these figures will undoubtedly increase pressure from Sinn Féin and others for a border poll, which will further increase unionist opposition to such a move at this stage.