What on earth happened?

What just happened?

Meetings in Brussels often run over. Maybe it's the witty repartee, or the chest-beating, or the fact that the institutions here are in the business of trying to get nearly 30 countries to agree on complicated issues. It is political rocket science.

But when Theresa May's lunch with Jean-Claude Juncker went on, and on, and on, and on, a whiff of doubt started to do the rounds.

• UK and EU fail to strike a deal

Through the morning, MEPs and senior politicians - including the president of the EU Council - were suggesting on the record that there had been enough compromises on the British side over the Irish border to enable the talks to move on.

Downing Street did little to dampen down what was much more than the usual kind of summit speculation.

There were well-known politicians in Brussels and in Ireland saying publicly they were confident and that there had been enough progress to move forwards.

But it seemed they hadn't reckoned on the determination of the DUP.

They have been kept in close contact with the government over what was being discussed. But after this morning's reports circulated they snapped.

The leader, Arlene Foster, called a press conference to reiterate her often stated position that in her view, Northern Ireland must not be allowed to be any different to the rest of the Britain as a result of Brexit.

Dramatic pronouncements

It is, of course, possible that the DUP feels the political need to be publicly cross as much as possible, before an eventual compromise.

Some familiar with their thinking claim this is in fact the case, and that this choreography with the dramatic pronouncements at Stormont are all part of the script.

But today their public ire made it nigh impossible for the PM to proceed. I'm told 20 minutes after Foster's press conference, she received a call from the prime minister, in which it was made plain that the DUP could not support the proposed deal.

They were not prepared to put up with something that looked like it was a victory for Dublin that was, in the DUP's view, ambiguous on Northern Ireland.

Theresa May had broken off her talks with Jean-Claude Juncker to hear that she would not be able to claim victory today. She then went back into the meeting, and shortly after made her grim statement alongside him.

Number 10 sources insist that it was not all about the DUP, saying citizens' rights are still to be completely resolved, as well as the issue of the border.

Not all over

But having moved mountains to please Dublin, the prime minister now has a big problem with her supporters in Belfast.

Most painful, perhaps, because her reliance on the DUP is a problem of her own making.

Had she not made the biggest mistake of her career in calling the election, they would not be able to call the shots.

It feels like a big blow for the UK government today because it is.

The prime minister would not have invested her own political capital by coming to Brussels today if the government didn't believe that a deal was highly likely.

It is deeply embarrassing, therefore, for her to go home empty handed. But it doesn't mean at all that it's all over.

Sometimes difficult negotiations even need a bust-up before a breakthrough.

Theresa May is likely to be back in Brussels later this week - she'll hope that tradition of near-defeat before eventual victory rings true this time.

And don't forget, this is only the end game of the first phase. Nothing about Brexit was politically going to be easy without a majority.

Day-by-day now, the government is finding out why.