By Colette McBeth
Political correspondent, BBC News
Ed Miliband (right) said he thought long and hard about competing with David
Both Ed and David Miliband have said their bid to be the next Labour Party leader will not affect family relations, but what divides the two brothers?
Ed Miliband had wanted to wait until next week to launch his leadership campaign but it seems his constituency party in Doncaster North had other ideas.
After he told them last night he was going to run, one excited member immediately put a message on her Twitter page.
"Delighted that Ed Miliband has told party members he is going to run for leader," it read. The secret was out.
To be fair, it was anticipated. Even by David, who after declaring his own hand was immediately asked about Ed.
His response was that brotherly love was stronger than politics. In return Ed believes the contest won't drive a wedge between the two men.
Both went to Haverstock School in Camden, a comprehensive. Both studied the same degree at the same Oxford College and served in Gordon Brown's cabinet together
He said he had thought long and hard about his decision but both he and his brother agreed that the party needed the widest possible choice in the contest.
The brothers were born four and a half years apart and grew up in north London.
Their late father, Ralph, was a Marxist intellectual who arrived in Britain in 1940, fleeing the Nazi advance into his native Belgium.
Both went to Haverstock School in Camden, a comprehensive.
Both studied the same degree at the same Oxford college and served in Gordon Brown's cabinet together - the first brothers to have done so since 1938.
But there are differences between them too. David was Tony Blair's head of policy and seen as a politician of government.
Ed on the other hand was an adviser to Gordon Brown, and has support among the party and the unions.
Although he served as energy minister under Gordon Brown, some MPs feel it is Ed who would mark a bigger break with the last administration than his elder brother.
MPs have already started receiving calls from the Ed and David camps
But David is the one who is better known outside the party.
One Labour backbencher put it like this: "The feeling is that Ed has the capacity to be a stronger candidate but there is a sense that he's not completely grown into it yet.
"David was widely seen to have been a very good foreign secretary and is respected on the world stage but may appear a bit geeky."
One supporter of Miliband Senior says he believes David can appeal to the party's traditional core vote but also win back votes from the middle ground, the very ones needed to ensure electoral success.
Both the Ed and David camps have already started canvassing support.
Some MPs have received personal calls from Ed, others have been called by the former Department for Environment, Food and Rural Affairs minister Jim Fitzpatrick, on behalf of David.
One of the new intake of MPs said she had been contacted not just by Ed and David's supporters, but by those gauging support for Ed Balls and Andy Burnham.
"They all seem like nice people. I'm going to wait for a few weeks and see what they have to say and then make up my mind," she said.
The former Children's Secretary Ed Balls, the former Health Secretary Andy Burnham and John Cruddas, the MP for Dagenham and Rainham in east London, are all possible contenders.
But as one MP put it, it is the candidate who not only has the right policies but a down to earth way of communicating them to the public that deserves to be the new leader of the Labour party.