Helen Clark says if she was in charge, she would let the British teen who ran away to Syria to join Islamic State (IS) back into the UK.
In 2015 at the age of 15, Shamima Begum left the UK for Syria with two friends, desiring a life with the terrorist group.
She married an IS fighter and has just given birth to her third child - the only one alive so far. Now living in a Syrian refugee camp, she says wants to return to the UK, which under international law is obliged to take her back.
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Ms Clark, a former New Zealand Prime Minister, says Begum was "groomed like a paedophile" and "has a right to go home".
"She is a UK citizen, she's born there. The head of (intelligence agency) MI6 says she has a right to return," she told Newstalk ZB on Monday.
"It's always possible that people can turn their lives around. We've seen that before."
Ms Begum has been criticised for an interview she gave to Sky News this week claiming there's no proof she did anything dangerous.
"I think a lot of people should have sympathy towards me, for everything I've been through," the 19-year-old said. "I can't live in this camp forever."
Ms Begum said she had had a "good time" with Islamic State.
"I don't regret it because it's changed me as a person," she said. "It's made me stronger, tougher. I married my husband. I wouldn't have found someone like him back in the UK."
Her husband has surrendered to Syrian fighters allied to the United States-backed Syrian Democratic Forces.
Ms Clark says Ms Begum "behaved extremely badly" and should be under watch for the rest of her life.
"I'm appalled by the 'no regret' attitude she showed," she told Newstalk ZB.
"But nonetheless she is a citizen, and in the end we do have obligations to citizens."
But debate continues in the UK as to whether to help Ms Begum. The UK government says it will not risk any lives to help Britons who have joined a banned terrorist group.
And writing in the Sunday Times, Home Secretary Sajid Javid warned he would "not hesitate" to prevent the return of Britons who travelled to join IS.
"The difficult challenge we now face is what we should do about those who are still seeking to return," he said.