David Cameron's been criticising him all week and attempted to stop him from getting his new job, but now the prime minister has called Jean-Claude Juncker to congratulate him for securing the nomination to be the next president of the European Commission.
The former Luxembourg premier told the Prime Minister he was "fully committed" to finding a solution to British concerns about the European Union and they discussed "how they would work together" to boost competitiveness, according to No 10.
It comes after a weekend of recriminations following Mr Cameron's defeat in his bid to stop the arch-federalist from taking the EU's top job.
A Downing Street spokesman said: "The Prime Minister called the Commission President-designate, Jean-Claude Juncker, this afternoon. The Prime Minister congratulated Mr Juncker on running a successful campaign and securing the Council nomination.
"They discussed how they would work together to make the EU more competitive and more flexible. The PM welcomed Mr Juncker's commitment of finding a fair deal for Britain and Mr Juncker said that he was fully committed to finding solutions for the political concerns of the UK.
"The PM wished Mr Juncker well with the hearings in the European Parliament and they agreed to speak further at the next European Council on 16 July."
Labour said the failed negotiations over the appointment had been a "catastrophe" for Britain.
The party is attempting to keep up the pressure on the Prime Minister over the defeat, which it claims has taken the UK closer to the "exit door" that could put three million jobs and tens of thousands of businesses at risk.
Business leaders have also warned that the country's economic success depends on it remaining a full member of the European Union.
But William Hague refused to be drawn on whether pulling out of the EU would be a disaster, insisting the decision was "up to the British people".
The Foreign Secretary said it was "far too early to say" if the Government would fail in its bid to renegotiate Britain's relationship with Brussels.
"The Prime Minister acknowledged that the task had got harder when he spoke after this on Friday," he told BBC One's Andrew Marr Show.
"But look at the track record of the last few years. He is the first Prime Minister to negotiate an actual reduction in the European budget."
Asked if it would be a disaster to exit, he replied: "This will be the debate in the referendum. I have always argued against more power going to the European Union but for us to be a member of Europe but not run by Europe.
"The British people will decide in a referendum whether that is sustainable or not."
Mr Hague refused to comment on claims that Mr Juncker is a heavy drinker amid claims in The Mail On Sunday by an anonymous former Tory foreign office minister that the former Luxembourg prime minister drinks so heavily he "dribbles" during meetings and is often "incapable of working after lunchtime".
"I'm not going to go into any personal matter about Jean-Claude Juncker or anybody else," he said.
Shadow chancellor Ed Balls said he had "never seen a negotiation so cack-handed".
"We won't be influential in the world, unless we are influential in Europe," he told Marr.
"What is David Cameron's European policy? Does he think we should be in Europe? I do. I think that we will only be influential in the world if we are influential in Europe. Does he want reform? He says he does but he can't tell us what his reforms are.
"He's set an arbitrary timetable for a referendum which everybody knows is deeply destabilising and why has he done that, because his European policy is not being decided by the national interest, Britain's future, jobs and investment, but by what Tory backbenchers are demanding.
"He's weak, he's lost control, he's on the back foot, Britain is suffering. I think it's catastrophic for Britain."
CBI director general John Cridland told The Observer: "The EU is our biggest export market and remains fundamental to our economic future. Our membership supports jobs, drives growth and boosts our international competitiveness."
He dismissed the idea that Britain could be just as successful outside the EU with some form of associate membership status, a suggestion favoured by some Conservatives.
He said: "Alternatives to full membership of the EU simply wouldn't work, leaving us beholden to its rules without being able to influence them. We will continue to press the case for the UK remaining in a reformed European Union."