Gordon Brown today promised his "full, unequivocal and tireless support" to his successor as Labour leader.
The former Prime Minister made his first appearance at a major Labour event since stepping down as leader in May to speak to delegates at the special leadership conference in Manchester, moments before the announcement of the name of his successor.
He arrived on stage with wife Sarah following a video looking back on his record as Chancellor and Prime Minister.
To tumultuous applause, Mr Brown told delegates: "We are Labour, we will always be Labour and will never be anything other than Labour."
And he said: "I stand here today not so much to lay down my role as leader of your party, but to renew my commitment to our party as an ordinary member.
"I'm here today not to walk away from my responsibility for what happened at the election, but to take full responsibility.
"I take the whole fault on my shoulders alone. And it's right for this party to get out of what we are worst at - the blame game - and into what we are best at - the future business."
Mr Brown said that whoever won the election would have his "full, unequivocal and tireless support".
"In all the months and years to come, you will not find me - not now, not ever - doing anything other than supporting the Labour team," he said.
The Labour Party was "the keeper of hope, the guarantor of justice, the custodian of aspiration and now clearly the only progressive party that this country has", he said.
Mr Brown paid tribute to Harriet Harman, his deputy who took over as Labour's acting leader when he stepped down in May, as well as his predecessors as leader John Smith, Neil Kinnock and Tony Blair.
And - in an echo of her tribute to him as "my hero, my husband" - he said: "More than anything I want to thank, for a love affair that will never end, my wife, my hero, Sarah."
Mr Brown also gave his thanks to "the two most important men in my life - my sons John and Fraser". In a joking reference to Lord Mandelson's memoirs, he added: "To them, I am the third man."