British lawmaker David Miliband, who lost the 2010 battle for the leadership of the opposition Labour party to his younger brother Ed, is to stand down as an MP, it was reported on Monday.
David Miliband, who was foreign secretary in Gordon Brown's government, quit front-line politics after his bruising defeat.
He will now leave his post as representative for the northern England seat of South Shields, which he has occupied since 2001, the Daily Mirror reported.
The BBC later reported he was heading to New York to become head of the International Rescue Committee, a charity which responds to humanitarian crises worldwide.
The two brothers, sons of Marxist theorist Ralph Miliband, have publicly denied falling out over the leadership vote, but David has missed his younger brother's last two speeches at the Labour Party's annual conference.
He said his decision "to step back" from front-line politics was taken in order to avoid "the daily soap opera" of working with his brother.
Labour MP Keith Vaz paid tribute on Twitter, writing: "Stunned by the news about David Miliband. A huge loss to British politics. The best and the brightest leaving the country."
Fellow MP John Woodcock added: "David will be brilliant over the water as he always is. He's an inspiration; know he'll be back in fight one day but for tonight am just sad".
It had been rumoured that he was about to make a political comeback after launching a scathing attack on the government's welfare reforms, and with his brother assuring him "the door is open".