David Miliband told ITV News "I am leaving politics" as he steps down as an MP to take on a charity role based in New York.
He admitted life had been tough since losing the leadership election to his brother Ed.
Political Editor Tom Bradby began by asking him whether the move means an end to his political career:
The former Foreign Secretary David Miliband has told ITV News: "I am leaving politics."
He told political editor Tom Bradby it is "not fair for me to spend my time looking backwards and inwards" about losing the Labour leadership election to his brother Ed.
He denied any falling out with his brother: "We fought a leadership election but we don't fight each other, Ed and I. That's not the Miliband way."
But he admitted: "Is it tough? Of course it's tough."
He said he "kept him [Ed] informed" about his new role.
Ed Miliband has said the "door was open" for his brother David to return to front line politics but he has taken the decision to take on a new role based in New York. The Labour leader said his brother will be "serving the world" with his new charity position:
David Miliband has published his letter of resignation on his website. In it he says that following the leadership election - in which he lost out to brother Ed - he said he took a role on the "frontline" in order to give his brother space and the ability to lead "without distraction".
He said: "As you know, I see every day the damage this shocking government is doing to our country, and passionately want to see Labour back in power.
"After the leadership election, I felt I could be most helpful to the party on the front line, in South Shields and around the country, rather than on the front bench in Parliament.
"I felt this gave Ed the space and at the same time the support he needed to lead the party without distraction. He has done so with real success, leading a united team that has taken the fight to the Tories.
"I am very pleased and proud that our shared goal of making this a one-term government is achievable."
A man from South Shields has been arrested in connection with alleged threats to shoot 200 schoolchildren in America.
It follows an anonymous post on a memorial page on Facebook on Wednesday 6th February.
Northumbria Police have confirmed a 24-year-old man has been arrested on Friday on suspicion of making threats to kill and is currently in custody.
A spokesperson for the force also said there is currently nothing to suggest he posed any physical threat to schools in the UK or in America.
A father who bit off part of a love rival's finger at a children's nativity play in South Shields has been sentenced to 11 months in jail.
40-year-old Lee Wilkinson fought with Michael Dent at Harton Primary School in December 2011 during which he bit off the tip of Mr Dent's left little finger.
The court heard that the pair had been involved in a long-running feud after Mr Dent had an affair with Wilkinson's wife while he was working away.
Passing sentence Judge Simon Hickey said he was unable to suspend sentence because of the nature of the offence.
Wilkinson admitted wounding and a public order offence.