Arlene Foster revealed she spoke with the incoming prime minister soon after his victory was declared – and that she immediately put him on notice.
But she added: “That agreement included a review between each parliamentary session.
“This will take place over the coming weeks and will explore the policy priorities of both parties for the next parliamentary session.”
Mr Johnson will need the support of the DUP even more than his predecessor did, as even the flimsy working majority she negotiated with the Northern Ireland party crumbles.
He will inherit a majority of just two – including the 10 DUP MPs – which will fall to only one if, as expected, the Liberal Democrats win the Brecon and Radnorshire by-election next week.
Some of his aides are already wargaming a snap autumn general election, as the likely only way to meet his pledge to leave the EU on Halloween, “deal or no deal”.
In a statement, Ms Foster said: “I have spoken with Boris Johnson and congratulated him on becoming leader of the Conservative Party.”
And she added: “I also look forward to welcoming Mr Johnson back to Northern Ireland shortly after he becomes prime minister.”
Mr Johnson is widely expected to carry out a whistlestop tour of Edinburgh, Cardiff and Belfast in the coming days, to emphasise his commitment to preserving the United Kingdom – which could be threatened by Brexit.
The DUP refused to back the Brexit withdrawal deal because it feared the threat to the union from the Irish backstop, so will expect the new prime minister to stick to his vow that it must be “junked”.
Mr Johnson has already been keen to stay close to the party, speaking at its conference last year and securing a Stormont photo with Ms Foster a few weeks ago.
Significantly, he has vowed to end prosecutions of veterans who served in Northern Ireland, pledging to bring forward legislation before the next general election.
He also said it would not be “the end of the world” if power-sharing at Stormont was not restored before Brexit, although that would probably require direct rule from Westminster – likely to anger nationalists.
The Independent revealed last year that the £1bn “cash for votes” money was being handed to Northern Ireland without the promised full Commons scrutiny.
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