European Commission President Ursula von der Leyen will meet with the King Charles at Windsor Castle on Monday afternoon.
It comes as Rishi Sunak is poised to agree a post-Brexit deal with the EU chief to resolve the ongoing row over the Northern Ireland Protocol.
If the final text is agreed at talks this lunchtime, Mr Sunak is expected to hold a press conference with Ms Von der Leyen later this afternoon before heading to the Commons to deliver a statement.
A Palace spokesperson said: “The King is pleased to meet any world leader if they are visiting Britain and it is the government’s advice that he should do so.”
Unionists in the DUP and hardline Tory Eurosceptics were angered by the move when it emerged Ms Von der Leyen was set to meet the King on Saturday, before it was cancelled for operational reasons.
The DUP’s Sammy Wilson and others said it risked dragging the monarchy into a political announcement, with the unionist party expected to oppose any Brexit deal which maintains a role for EU law and courts.
Jacob Rees-Mogg said it would be a mistake for Ms Von der Leyen to meet the King before MPs approve the protocol deal, following suggestions it could even be called the “Windsor Agreement”.
Mr Wilson, the DUP’s Brexit spokesperson, it would be “a cynical use, or abuse of the king” – saying it would mean Mr Sunak was “dragging the king into a hugely controversial political issue, not just in Northern Ireland but even within his own party”.
But No 10 rejected the idea of drawing the monarchy into the Brexit deal. “It would be wrong to suggest the king would be involved in anything remotely political,” a government source said at the weekend.
Deputy PM Dominic Raab made it clear on Sunday that there was “no de facto veto” for the DUP, the unionist party that is still expected to oppose the compromise.
Mr Rees-Mogg put Mr Sunak on notice of a possible Tory revolt if the DUP does not support the deal – claiming that the support of both Mr Johnson and the DUP were vital.
He told GB News: “It will all depend on the DUP. If the DUP are against it, I think there will be quite a significant number of Conservatives who are unhappy.”
However, several senior Tory Brexiteers told The Independent they were minded to support the deal and expected Mr Sunak to sign the agreement without the backing of the DUP or ERG.
Former Brexit secretary David Davis said his own “instinct” was to support a deal, and that he expected a rebellion of hardliners to be limited to a few dozen hardliners. “I think the idea of 100 rebels is absolute nonsense,” he said.