It is a scenario that unionists have wondered about for decades, but which has never come to pass.
Since the formation of Northern Ireland over a century ago, unionist MPs have never held the balance of power in quite the way that they do now.
There were many narrowly divided parliaments in the decades after the Second World War but the Ulster Unionists then were effectively a part of the Conservative Party and voted in the House of Commons under the Tory whip.
The February 1974 parliament was hung but the number of seats by which Labour and the Tories fell short was greater than the number of unionists. In 1992-7, the Tories needed unionist votes only at the end, but did not pursue a pact.
Now it has happened, and – as the history above shows – a rare scenario that happens every 50 years or less.
It is unclear what was discussed yesterday, but we will find out today if there is a final agreement. Arlene Foster did the right thing when she said on ITV News after the meeting that Brexit and counter-terrorism measures were part of their demands, knowing that that will resonate with Middle England.
Given the suspicions there are of unionists among the general public in Britain (many of whom will know very little about unionists) that sort of talk will reassure millions of people.
The DUP leader was also right to dismiss “nonsense” that has been peddled about the party’s approach to social questions.
As the Ulster Unionist gay rights pioneer Jeffrey Dudgeon wrote in an article for the think tank Policy Exchange, republished in shortened form opposite and on our website in full, the DUP stance on such matters is now nuanced.
Mrs Foster distinguished between hostility to gay people and opposition to same sex marriage in a way that will command widespread sympathy in Great Britain, even among people who take a different view but respect individual moral standpoints.
It seemed a good first day to the Tory-DUP understanding yesterday, but there is a long way to go in settling this deal.