Andrea Leadsom has been the victim of a "stitch-up", Iain Duncan Smith has claimed, following the outcry over her comments about motherhood.
Leadsom's suggestion, in an interview with The Times, that she was better qualified for the role of prime minister because she is a mother, and Theresa May is not, sparked fierce criticism.
Duncan Smith is backing the energy minister to succeed David Cameron and he told Peston on Sunday that there had been "a black-ops" operation to destroy Leadsom, who he described as a "decent, honourable person".
He said she was "genuinely mortified" by the fallout to her interview.
"I've been around in politics long enough to see plenty of incredibly experienced cabinet ministers and prime ministers get stitched-up in the course of an interview," the former Tory leader said on Peston on Sunday.
"I think what they, The Times, was very clear: they wanted to have a story about her family vs Theresa and that's essentially what they got."
"The question is did Andrea at any stage beleive that she was in the business of trying to contrast her family background with that of Theresa's and I don't believe that. I've talked to her and she's mortified - genuinely mortified."
He said "talking about your family shouldn't be a crime in politics".
Leadsom said she was "disgusted" by the way her comments had been presented and insisted that she believed "everyone has an equal stake in our society".
But she faced calls to withdraw from the Tory leadership race with Business Minister Anna Soubry saying the controversy proved she was "not PM material".
Employment minister Priti Patel, who campaigned for Brexit alongside Leadsom, told the Sunday Telegraph that she feared the energy minister could become the Tory equivalent of Jeremy Corbyn because of her lack of support in Parliament.
Baroness Warsi told Peston on Sunday that she believes it was a "slip of the tongue" but raised concerns about her judgment.
Tim Loughton, Leadsom's campaign manager, said Leadsom was a "fresh face" who the establishment were "ganging up on".
"The establishment are ganging up... it's all about 'let's gang up on Andrea'," he told the BBC's Andrew Marr Show.