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.
David Miliband was nearly Prime Minister, and nearly Labour party leader, but his brother's rise has led him to take a back seat.
David Miliband will resign as an MP to take up a job in America, a move which is set to be announced today.