David Miliband today said he was "incredibly proud" of his brother Ed who beat him in the race for the Labour leadership.
With the shadow foreign secretary considering his future following Saturday's narrow defeat he told the Labour Party conference he was "honoured and humbled" by the support he had received.
"Ed is a special person to me. Now he is a special person to you," he told delegates in Manchester.
The shadow foreign secretary has not yet revealed whether he will stand for election to serve in his younger brother's shadow cabinet.
Mr Miliband was not originally scheduled to make a formal speech today, but revealed he had been asked last night to address conference.
Making a joke about his defeat, he said: "As it happens on my computer, in a couple of files marked 'Saturday, version seven' and 'Tuesday, version 23' it just so happens I've got a couple of speeches to draw on this morning.
"But don't worry, I'm not going to give them."
He told the conference: "I've been incredibly honoured and humbled by the support that you have given me. But we have a great new new leader and we all have to get behind him.
"I'm really, really, really proud. I'm so proud of my campaign, I'm so proud of my party but above all I'm incredibly proud of my brother.
"Ed is a special person to me. Now he is a special person to you and our job is to make him a special person for all the British people."
Mr Miliband said: "You don't run for the leadership, you don't do anything like that in politics or in life, unless you are 100% committed to winning.
"But I've also learned something else in life: you never go in for something, especially something so important, unless you are sure in yourself that you are reconciled to the prospect that you might lose. That's life.
"So to those of you who have been coming up to me in the last few days - don't worry, I'll be fine."
He joked that at a reception for the Usdaw union a man told him: "Ed, congratulations on your victory." Mr Miliband told the conference: "I can do without that."
Mr Miliband, who received a standing ovation after his address, issued an appeal for an end to Labour's "soap opera" politics, insisting that the party would not win elections unless it was united.
"When people look back at this conference in Manchester, let us vow today that they will say two things," he said.
"First, the Labour Party learnt its lessons. It learnt to listen to the British people and it learnt, above all, that, unless we are united, we will lose.
"And I say today: no more cliques, no more factions, no more soap opera. One united Labour Party taking on one divided Government.
"There's a second lesson - and it's whether we spend our time looking inwards and backwards, or spend our time looking outwards and forwards.
"Let historians look back on our conference in Manchester and say this was the conference where Labour looked forward, not just to its own future but we looked forward to the future of Britain.
"That is our task at conference all of this week. We are a party that doesn't just examine our own navel, doesn't just sort out our own leadership.
"It's in touch every day with the people of Britain, concerned with their concerns, fighting for their issues and fighting for a cause that is very very special."
Mr Miliband cited Labour's fourth leader, John Robert Clynes.
"He said 'We come into Parliament not to practise a class war, but to end it'."
Mr Miliband paid tribute to British troops serving in Afghanistan.
"We need to come out from this conference unified, and nowhere is that more important than in the war in Afghanistan," he said.
He said the Armed Forces were "the best and bravest of British - and we should be so, so proud of what they do for our country".
The former foreign secretary said the "civil war" in Afghanistan would not be brought to an end by military means but only via a political settlement.
He urged the Labour Party to support Prime Minister David Cameron's attempts to achieve that.
"Let's send a serious message to David Cameron, a message from us as British people to him as British Prime Minister - when he takes, as I hope he will, risks for peace, we will be the first to congratulate him every step of the way," Mr Miliband said.
He criticised that "post-imperial delusion" that the rest of the world would "speak to us because we are Britain", adding: "People will talk to us when we have strong alliances around the world."
He said those alliances started in Europe and spread to the US.
"It's not the opposite of an independent foreign policy to choose to work with (US) President (Barack) Obama and Secretary (of State Hillary) Clinton. It is an independent foreign policy that says that Britain's values and interests are best pursued with a superpower whose leaders do share our values and interests."
But he criticised Mr Cameron's strong pursuit of commercial interests via Britain's network of foreign embassies.
"There is another delusion that we have to take on and that is the delusion that we reduce British diplomacy to being simply a group of sales people extending British trade," he said.