David Miliband pleaded with Labour today not to turn the leadership struggle into the kind of "soap opera" that disfigured the Blair and Brown era.
Making his first appearance on the conference stage in Manchester since his narrow defeat, the shadow foreign secretary called on the party to unite behind younger brother Ed.
But he also fuelled speculation over his own future by failing to commit to serving on Labour's top team.
Mr Miliband received a warm welcome when he emerged this morning to face the party that rejected him, with his brother joining the standing ovation from the platform.
Thanking delegates for their expressions of sympathy, he quipped that one had mistaken him for Ed and offered congratulations, adding ruefully: "I can do without that."
He also joked that the short notice for his speech today had not been a problem - because he already had some unused drafts lying around.
But Mr Miliband made clear that he had no intention of being a thorn in the side of the new leadership despite his obvious disappointment.
While he had been "100% committed" to fighting for the leadership, he had gone into the contest "reconciled to the prospect" that he might lose, he said.
Referring to the Blair-Brown conflict that constantly threatened to tear the party apart during its 13 years in power, he insisted: "No more cliques, no more factions, no more soap opera - one united Labour Party taking on a divided Government."
"We have a great new leader and we all have to get behind him," he said. "I am really, really, really proud. I am so proud of my campaign. I am so proud of my party. But above all I am incredibly proud of my brother.
"I see Ed as 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."
The brothers, who were earlier seen chatting privately at a cafe in the conference centre, embraced after the address.
When they came off stage David reportedly needed to comfort his wife Louise, who was in floods of tears.
The gathering in Manchester has been dominated by speculation over the former foreign secretary's intentions, and possible jobs that he could seek outside of UK politics.
Mr Miliband has until 5pm on Wednesday to decide whether to put forward his name for the shadow cabinet elections, which are expected to involve 50 or more MPs chasing 19 slots around Mr Miliband's top table. The results of the poll are due on October 7.
Ed Miliband this morning indicated that he will not make any announcement on appointments until next week at the earliest, and said that David should be given time to "make his own decision about the best thing for him".
Dismissing reports of tensions with his elder brother, he said: "There is no psycho-drama. David and I have been extremely close during this contest, before the contest and after this contest, and the graciousness he has shown since Saturday speaks volumes about him as a person."
The new Labour leader praised his brother's "great and inspiring speech". "I think it shows the determination this party has to unify going forward and unify as a team," he added.
Attention at Manchester was turning towards the issue not only of whether David Miliband or third-placed leadership contender Ed Balls may be offered the post of shadow chancellor, but also of whether the new leader is planning a shift in economic policy.
Ed Miliband yesterday said that he regarded Alistair Darling's plan to halve Britain's deficit within four years as a "starting point" which he hoped to "improve" on, leading to speculation that he might scale back the cuts envisaged by the former chancellor.
Mr Darling, who is standing down from the shadow cabinet, told delegates today that he was confident Mr Miliband would maintain a "credible" plan which kept Labour on the "centre ground".
"We cannot ignore the deficit. That would be as foolish as standing back and doing nothing when the crisis hit," he said. "We had in place tough plans to halve borrowing within four years."
Delivering what is likely to be his final speech to conference as a frontbencher, Mr Darling went on: "Our approach is measured - and balanced. What we did over the last two years has worked. That's why our economy is growing, why borrowing is coming down.
"To abandon that balanced approach, as the Tories and Liberals are doing, will put tens of thousands of jobs at risk, and hit the living standards of millions of families in this country.
"But as Ed has said on Saturday, if we set out a credible plan, with conviction and confidence, we can win back the trust and support we lost in May."