David Miliband launched his bid to lead the Labour Party today and called his brother and rival for the post "a huge talent".
The 44-year-old former Foreign Secretary said he was "very proud" of his younger brother Ed.
Speaking at the Customs House in his constituency of South Shields, South Tyneside, Mr Miliband spoke fondly of his Marxist father Ralph.
"'My oh my,' he must be thinking 'what did I do wrong? Two MPs in a Labour Cabinet'."
The father-of-two professed his pride in his wife and sons, adding: "I'm proud of my brother too as someone of huge talent, really proud."
The brothers have vowed to remain close despite being rivals for the Labour leadership.
He said their mother, who believed passionately in causes, will have to abstain for the next few weeks.
Mr Miliband said Labour must "reform, repair and reconnect in Opposition" and that required new leadership.
Yet he praised the two leaders he hoped to follow, saying: "Tony Blair over 10 remarkable years and Gordon Brown, with historic courage, ability, insight, in three very difficult years have made Britain better."
He vowed to leave behind the Blair/Brown rivalry, adding: "New Labour did fantastic things for the country, never let anyone take that away, but what counts is Next Labour."
In a 25 minute speech, which ended with a standing ovation from the audience and a hug from wife Louise, he stated he would run a clean campaign, without negative briefings against his rival candidates.
After the speech, Mr Miliband insisted the contest would not damage his family.
He said: "Our family is more important than politics and we are absolutely determined that it won't get in the way.
"Ed is extremely talented and has made his own decision to run.
"He is going to be a brother I love at the end of the campaign, whatever happens.
"My mum is not the abstaining type but she's abstaining on this one."
Asked if Next Labour, a phrase from his speech, would be the new slogan, he replied: "We are proud of what we have achieved, we are humble about our mistakes but we don't want to live in the past.
"Next Labour is about listening and engaging first, then giving real shape and real substance to the offer we are going to make to the public at the next general election."
He said the lesson from Tony Blair and Gordon Brown's leaderships was they were best when at "their most authentic".