BREXIT negotiations will now enter the "tunnel" phase of intensive and secretive talks in a major boost for Boris Johnson's prospects of brokering a fresh deal.
EU Council President Donald Tusk said on Friday morning that "the United Kingdom has still not come forward with a workable, realistic proposal" but tempered that by saying that "even the slight chance (that a deal can be struck) must be used".
Downing Street is understood to have shared details of the proposed compromise privately with European Union negotiators, which paved the way for detailed formal talks to begin ahead of next week's meeting of European Union leaders.
Mrs. Foster issued the statement a few hours after Boris Johnson refused to rule out leaving Northern Ireland in the E.U.'s customs union while the rest of the United Kingdom would leave it.
Michel Barnier, the European Commission's Chief Negotiator, had a constructive meeting this morning with Steve Barclay, the UK Secretary of State for Exiting the EU.
In a statement on Friday, Arlene Foster said that, while negotiations are a matter for the UK Government, the DUP will "exercise our considerable influence" to "stand up for Northern Ireland" and will only ever support arrangements that are in province's long-term economic and constitutional interests.
"Brexit is like climbing a mountain".
"We need vigilance, determination and patience", Barnier told reporters on his way to debrief European Union ambassadors and Parliament's Brexit group.
Earlier this week, several senior European Union figures played down the chances of Brexit happening with a deal agreed to by both sides.
He said the United Kingdom had yet to put forward an "operational, legally binding solution" to replace the Northern Ireland backstop - meant to prevent the return of a hard border with the Republic. If it is time for the sake of time?
Mr Barclay and Mr Barnier were dispatched after the two prime ministers held face-to-face discussions in the Wirral yesterday, prompting the leaders to "see a pathway" to a possible agreement.
Barnier's team has been in "technical talks" with British officials for some time, but these were not making enough progress towards a treaty text that could forestall a chaotic "no-deal" Brexit in three weeks.