Ed Miliband, 40, is the first British political leader of a major party to be living with his family out of wedlock, reports Daily Mail.
Miliband and his partner Justine Thornton, who will give birth to the couple’s second child in little over a month, have not tied the knot. In fact, Miliband's name isn’t even listed on his 15-month-old son’s birth certificate, the newspaper claims.
The couple’s relaxed stance on marriage stands in contrast to David Cameron and Nick Clegg’s ultra-traditional set-up.
Miliband's surprise win also reflects the changing attitude of British voters. Earlier, being part of an unmarried couple was considered electoral suicide.
Labour elects Ed Miliband as new leader
Britain's opposition Labour Party chose former Energy Secretary Ed Miliband as its new leader on Saturday after a cliffhanger vote.
Miliband, 40, defeated his older brother David, a former foreign secretary, by a wafer-thin margin to take over the helm of the centre-left party.
He succeeds former prime minister Gordon Brown who resigned after the party lost the May election, ending 13 years in power.
David Miliband was favoured by centrists in the party whereas Ed has slightly more left-leaning views and won the backing of major trade unions who help finance the party. Miliband won in the fourth round of the vote count, by a margin of a little over one per cent, to steal the prize that had seemed within the grasp of his older brother for much of the leadership campaign.
"David, I love you so much as a brother and I have such extraordinary respect for the campaign that you ran - the strength and eloquence that you showed," Miliband said in a heartfelt message to his brother.
"I have to unify this party and I will," the winner, who was propelled to victory by strong union backing, told party activists gathered for their annual conference in the northwestern city of Manchester.
"Today the work of the new generation begins," he said.
The new leader's focus will be on fighting deep public spending cuts planned by the ruling coalition which Labour says threaten public services and will hit the poor hardest.
The Conservative-Liberal Democrat coalition formed after the May election blames Labour incompetence for Britain's record peacetime budget deficit and says it must take urgent action to eradicate it or risk a loss of investor confidence in Britain.