Ed Miliband tonight hailed his brother David's decision to quit the shadow cabinet as a "thoughtful and gracious" decision, adding that the door was open for him to return to Labour's frontline.
Speaking on the steps of the Midland Hotel at the Labour Party conference in Manchester, Mr Miliband said he had spoken to his older brother earlier about the decision.
He said David had been "thoughtful" in terms of his family and "gracious" about the future of the Labour Party.
"He is my brother and I am very clear that, as leader of this party, my door is always open for him to serve in the future, either in opposition or back in government," he said.
Ed Miliband, who defeated David to become Labour leader on Saturday, said: "While it would obviously have been fantastic to have him serving in my shadow cabinet, I think he has made a thoughtful and gracious decision.
"Thoughtful for his family and the time he can have with them, and gracious in terms of the future of our party."
Mr Miliband said he would have had a "stronger team" with his brother in the shadow cabinet but said he had "100% respect" for his decision.
He said it was "absolutely right" that his brother had taken his time over making the choice.
"I think it was a typically thoughtful, mature and gracious decision that he has made and it's one I 100% respect."
Asked whether Labour was "diminished" by his older brother's decision, Mr Miliband said: "He is a massive talent for our party and indeed for our country and I'm certainly not going to hide that fact. he is my brother and I have the hugest regard for him.
"We would have been a stronger team with him in it.
"But I think he is right to have made the decision he did, it's the right decision for him and he's made a judgment about what is the right decision for him and also, crucially, about the right decision for his party.
"He didn't want to see a repeat of some of the things we have seen in the past and I understand the reason for that.
"As for my feelings, I'm obviously delighted to be leader of this party but I'm obviously disappointed for him.
"That is the paradox, in a way, of this contest."
Asked whether he had "crushed" his brother's "political dreams", Mr Miliband said: "David was absolutely right when we first discussed this.
"He said 'It would be quite wrong for me to stand in your way' and I said to him 'Likewise' and we both said at the time 'May the best person, man or woman, win this contest'.
"I think that David has a big future in whatever he chooses to do in politics. My door is always open and I look forward to the possibility of him serving us back in government again."
Conservative Party chairman Baroness Warsi claimed David Miliband had quit because of political differences with Ed.
"David Miliband was a leading architect of New Labour. The fact that he doesn't want a place in Ed Miliband's shadow cabinet speaks volumes about the direction in which the new leader is taking Labour," she said.
"After being elected by the unions, this is further evidence that Ed Miliband is vacating the centre ground of British politics."
But a string of Labour frontbenchers emerged to say David Miliband had made the right decision for the party.
Tessa Jowell told the BBC: "He has done the right thing for himself, and for his family, and he has definitely done the right thing for the party. This has now given his brother Ed the space to run the party."
Shadow justice secretary Jack Straw said that even if Mr Miliband had taken "Trappist vows of silence" it would still have generated a story.
"That is the media we live with. Everyone in the media knows that is the case," he added.
He added: "The sensible thing to do is what David has done."
Shadow Welsh secretary Peter Hain took heart from the fact that he had left the door open to a return to the frontbench.
"The good thing is after recharging his batteries, he's left open that he might come back, like William Hague did after his sabbatical."
Shadow home secretary Alan Johnson said: "To remain in the shadow cabinet would invite constant scrutiny of their relationship and endless discussion of every nuance, however trivial.
"This decision will make it easier for Ed to flourish as leader whilst allowing David to pursue other political interests as well as working tirelessly for his South Shields constituents."
Former deputy prime minister Lord Prescott paid tribute to David Miliband, saying the party owed him "an enormous debt of gratitude".
"He helped create a record that we can be proud of and I respect the fact that during the leadership campaign he chose to defend it," he wrote on his blog.
Former home secretary David Blunkett said: "I believe that David Miliband is a man of honour. He has made the right decision for himself, his party and his brother.
"I promise him that it is possible to make a contribution outside cabinet and shadow cabinet, to still be heard where it matters and to think the unthinkable. I look forward to working with him from the backbenches in that role."
The chairman of South Shields Constituency Labour Party wrote to David Miliband praising his "courageous and selfless act of leadership".
Alan Donnelly made public his formal reply to the former foreign secretary's announcement, which said: "In South Shields we all realise how difficult the last few days have been for both Louise and you and it was quite right for you to take some time to consider the implications of the election result for your family and for the Labour Party.
"Ed and Labour's new parliamentary team must be free to focus all of their attention on challenging the coalition Government, and as you have recognised, your membership of the shadow cabinet at this time would simply act as a distraction.
"In withdrawing from the shadow cabinet elections today you are demonstrating a courageous and selfless act of leadership which, although very sad, I support completely."