Ed Miliband today formally declared his intention to stand for the leadership of the British Labour Party.
The former energy minister confirmed he will compete against his brother, David, during a speech in which he set out his vision for the future of Labour.
Mr Miliband told the Fabian Society in central London: 'I have talked to my family and friends and I have decided to stand to be leader of the Labour Party.'
Launching his campaign to applause, Mr Miliband called for a 'fraternal' contest for all candidates who put their names forward.
He said: 'My message to the British people is, we will learn from our mistakes, we will be part of your values again, we will be part of your community again and we will work with you to build the kind of country we want to see.
'And my message to our party is this: we have to use this leadership campaign as a first step on the road back to power because that is where we should be as a political party.
'It involves facing up to uncomfortable truths.
'I think it should be a fraternal contest, and not just in terms of myself and David but all the candidates at this election.'
Earlier, Mr Miliband joked that he could reveal the answer to the question of which brother his mother would choose to support.
'I do want you to be the first to know the answer to this because I think I can say that I am confident that, on the basis of her position on the political spectrum and on the basis of the runners and riders, that her candidate for the Labour leadership will be Jon Cruddas,' he quipped.
David Miliband is the only other candidate so far to have thrown his hat into the ring for the Labour leadership since Gordon Brown stood down on Tuesday.
It is expected that a number of other Labour Party members will declare their interest in standing over the next week.
Former children's minister Ed Balls told The Guardian that he would consult his local party before deciding whether or not to stand for the leadership.
Other potential candidates include backbencher Jon Cruddas and former health minister Andy Burnham.