European Union leaders are meeting in Brussels without David Cameron, in a highly symbolic portent of things to come.
After bidding an emotional farewell to EU summitry after his last trip to the Belgian capital as PM on Tuesday evening, Mr Cameron was not invited to join the prime ministers and presidents of the other 27 EU nations as they returned to the table to discuss how they will deal with the fallout from last week's Brexit vote in the UK.
Downing Street insisted that the PM's absence did not amount to a snub, saying that it accepted that the other member states would need to discuss the EU's stance in upcoming negotiations over the bloc's future relationship with the UK.
And in another glimpse of the changes which may be wrought on the UK by Thursday's vote, Scottish First Minister Nicola Sturgeon is travelling to Brussels for talks with European Parliament president Martin Schulz just days after setting in train the legal preparations for a possible second independence referendum to keep Scotland in the EU.
Mr Cameron flew back to London on Tuesday night after stepping off the European stage with an admission that public fears over immigration cost him last week's referendum and his job.
A clearly emotional Prime Minister said that there was "sadness and regret" among the 28 leaders around the table at the European Council that the UK was leaving the EU after 43 years, coupled with an acceptance that the decision of voters must be respected.
Getting the right solution on immigration would be a difficult challenge for the EU and "a major test" for the next PM - widely tipped to be Boris Johnson.
Mr Cameron was speaking after German chancellor Angela Merkel warned the UK must accept free movement if it wanted to retain access to the single market after withdrawal, as some non-members like Norway did.
Assuring the German parliament that she would not allow the UK to "cherry-pick" favoured elements of the EU package, she said: "If you wish to have free access to the single market then you have to accept the fundamental European rights as well as obligations that come from it. This is as true for Great Britain as for anybody else."
And there was continuing pressure for the UK to get formal separation talks under way, rather than waiting for months or years as some potential successors to the PM have suggested.
European Council president Donald Tusk said the bloc's leaders wanted UK exit plans to 'to be specified as soon as possible", while European Commission president Jean-Claude Juncker added: "We don't have months to meditate, we have to act."
Mr Cameron said he could not put a time frame on when his successor would get the ball rolling by invoking Article 50 of the Lisbon Treaty, which provides for a two-year negotiating period before a final divorce.
Over dinner with fellow leaders before flying back to London, Mr Cameron set out his assessment of the reasons behind Thursday's shock 52%-48% referendum vote for Brexit.
He told reporters later: "I think people recognised the strength of the economic case for staying, but there was a very great concern about the movement of people and immigration, and I think that is coupled with a concern about the issues of sovereignty and the absence of control there has been.
"I think we need to think about that, Europe needs to think about that and I think that is going to be one of the major tests for the next prime minister.
Asked if he now regretted calling the historic referendum, a sombre Mr Cameron said: "It's a sad night for me - I didn't want to be in this position. I wanted Britain to stay in a reformed European Union.
"At the end of the day I'm a democrat. I fought very hard for what I believed in. I didn't stand back. I threw myself in head, heart and soul to keep Britain in the European Union and I didn't succeed.
"And in politics you have to recognise that you fight, and when you win you carry on the programme, and when you lose sometimes you have to say I've lost that argument, I've lost that debate, and it's right to hand over to someone else who can take the country forward.
"Now of course I'm sad about that but I'm more concerned about Britain getting its relationship right with Europe.
"That is a far bigger thing than whether I'm Prime Minister for six years or seven years or what have you."