David Miliband was forced to deny plotting against his brother today amid claims of an ongoing feud over the Labour leadership.
The former foreign secretary called for the party to unite behind Ed, dismissing reports that he was hoping for him to fail as "soap opera".
"I have moved on from the leadership election and so should everyone else," Mr Miliband said in a statement. "Ed won, I stand fully behind him and so should everyone else.
"I called for unity last October and I repeat that now."
The latest wave of speculation over the brothers' relationship has been sparked by an unauthorised biography alleging that the fallout from last year's contest was far worse than either has admitted publicly.
David is said to have effectively accused his younger brother of lying about his conduct in the contest last year.
The revelations have fuelled doubts about Mr Miliband's future at the helm of the party amid criticism of his performance against David Cameron.
Last week's leak of a text of the victory address David Miliband planned to deliver - admitting Labour's economic stewardship had been flawed - did nothing to dampen rumours of divisions.
But in his statement today the elder sibling insisted: "We all have our part to play in supporting Ed and the frontbench team to ensure we expose this Government for its reckless policies that are damaging the country.
"The rest is soap opera of which I want no part and the public have no interest."
Ed will try to get back on track tomorrow with a keynote speech acknowledging that some voters see the party as having encouraged a "take-what-you-can approach" among benefit scroungers and millionaire bankers.
According to the book, written by two Labour-supporting journalists and serialised in the Mail on Sunday, Mr Miliband says he went to David's home and told him face to face that he intended to seek the leadership.
But the elder brother apparently denies that such a meeting ever took place.
The book also questions the idea that Ed made a last-minute decision to stand. Instead the former energy secretary is said to have been plotting to eclipse David for years.
The authors, Mehdi Hasan and James Macintyre, refer to reports that Ed tricked his sibling into not challenging Gordon Brown before the 2010 general election to boost his own chances of succeeding.
This is claimed to have sparked a separate rift between Ed and David's respective wives, Justine Thornton and Louise Shackelton. The book says Louise has been "nasty" to Justine and has "cut Ed dead".
The book, Ed: The Milibands And The Making Of A Labour Leader, asserts that the younger brother blames David's team for spreading his nicknames Red Ed and Forrest Gump.
It paints a less-than-flattering portrait of the young Ed, saying he was a "nasal, dull" youth and a "very unusual student" who had no girlfriends in his four years at Oxford and Harvard universities.
The brothers' Left-wing mother, Marion, who "could not stand Tony Blair", is said to have backed Brownite Ed for the leadership. She apparently believes the family will never be the same as a result of the row.
David can reportedly barely bring himself to speak to his brother now, and the two men communicate mainly through officials.
He is allegedly scathing about Ed's performance in private, saying he is "heading in the wrong direction".
For his part, Ed is said to regard his sibling as too "managerial and technocratic".
The authors also describe serious friction between Mr Miliband and his shadow chancellor Ed Balls.
The leader reportedly "dislikes" Mr Balls and has been overheard "slagging him off in colourful language" in the past.
Bizarrely, one of Mr Balls' own supporters is said to have warned Mr Miliband against putting him in charge of the crucial Treasury brief. They apparently suggested that if Labour won power he could end up with a "madman next door" in 11 Downing Street.
Bad blood between Mr Balls and Mr Miliband dates back to their days as advisers to Mr Brown, according to the book.
It claims Treasury officials divided the former Chancellor's backroom team into "girls" and "boys".
The "boys" included macho Mr Balls and rugged union fixer Charlie Whelan. The "girls" included the less aggressive Ed Miliband, fellow mild-mannered Brownite Douglas Alexander and respected policy aide Spencer Livermore.
"Ed and Alexander could often be overheard in their shared office 'slagging off' Balls, using colourful language," the book claims. "Their dislike for Ed Balls was an open secret."
The authors recount an extraordinary confrontation between Mr Miliband and Mr Balls in 2003, on the eve of the Iraq war.
Mr Miliband, who had taken a year off to study at Harvard University, apparently telephoned Mr Brown and urged him to resign over the war to force Mr Blair to quit.
But the suggestion was allegedly crushed by "dominant" Mr Balls, partly to humiliate "shy" Mr Miliband.
The claims could prove particularly damaging for Mr Balls, after leaks from a set of his personal documents highlighted his central role in rows over Mr Blair's departure from office.
There have been signs that the disclosure could have reopened old tensions between Blairites and Brownites in Mr Miliband's current team.
Posting on social networking website Twitter after the documents emerged, shadow communities secretary Caroline Flint said: "The last 5 Labour Leaders' Election Records: 0-1, 0-1, 0-2, 3-0, 0-1. Guess which one was Tony Blair? Enough said."
Although attempting to shrug off the book claims, neither Miliband camp has made much effort to suggest warm relations.
A source close to the Labour leader said: "David and Ed talked before, during and after the leadership election.
"There is no problem. This is tittle tattle and the Labour Party will be concentrating on meeting the challenges of Britain's future, not looking back to the past."
Blairite former Lord Chancellor Lord Falconer conceded that Mr Miliband's troubles were not all media-generated. "He is having the sort of difficulties that you always have in trying to break through when there is a new government," he told the BBC's Andrew Marr show.
Foreign Secretary William Hague twisted the knife by suggesting Ed was performing worse than he had as Tory leader between 1997 and 2010.
"I had quite a hard time as Leader of the Opposition," Mr Hague told Sky News' Murnaghan programme. "He seems to be doing worse in terms of making progress in local elections and so on."