The Sun newspaper has faced a backlash from domestic abuse charities for an article in which JK Rowling's ex said "I'm not sorry" for slapping her.
As part of a blog addressing criticism of her comments on transgender people, the Harry Potter author said her first marriage had been "violent".
Jorge Arantes told the Sun he slapped Rowling when she left him - but added "there was not sustained abuse".
The newspaper said it had not intended to "enable or glorify" domestic abuse.
Critics have accused the author of being transphobic for her response to an article about "people who menstruate".
Rowling said her personal experience of domestic abuse and sexual assault, and her concerns about protecting safe spaces for women, were some reasons why she spoke out about transgender issues.
The Sun's front page headline on Friday was: "I slapped JK and I'm not sorry".
Mr Arantes, who shares a daughter with Rowling from their marriage, told the paper: "Yes. It is true I slapped her. But I didn't abuse her." When asked about his response to her claims - which included that the relationship was violent - he said: "If she says that, that's up to her. It's not true I hit her."
Nicole Jacobs, England's domestic abuse commissioner, wrote to the newspaper to say she was "deeply concerned" about the story.
"It is unacceptable that the Sun has chosen to repeat and magnify the voice of someone who openly admits to violence against a partner," she said.
'Irresponsible and dangerous'
The charity Women's Aid said the newspaper's front page had a "negative impact", and added it was in conversation with the Sun about reflecting the voices of survivors of domestic abuse.
"Headlines matter," it added.
Some 20 anti-domestic abuse campaigners - including the chief executive of Women's Aid - wrote an open letter calling on the paper to apologise.
"Responding to a woman disclosing her experiences of domestic abuse and sexual assault by giving a platform to her perpetrator to trivialise the abuse he subjected her to is irresponsible and dangerous," the letter said.
Press regulator Ipso said it had received more than 500 complaints about the Sun article.
A spokeswoman for the Sun said: "It was certainly not our intention to 'enable' or 'glorify' domestic abuse, our intention was to expose a perpetrator's total lack of remorse. Our sympathies are always with the victims."
The spokeswoman added that the tabloid had a "long history of standing up for abused women", and "over the we have empowered countless victims to come forward and seek help".
Politicians have also criticised the Sun's coverage. The Liberal Democrats called on the Sun to donate the revenue made from Friday's newspaper to Refuge - while Labour's shadow minister for domestic abuse and safeguarding, Jess Phillips, said "doubt and disbelief" benefited perpetrators of abuse.
The sun headline is awful, the perpetrator more awful still. You'd be surprised how only his hideous arrogant admission will allow some to believe. Still too often doubt and disbelief are the best weapon abusers have in their arsenal... "no one will believe you."— Jess Phillips MP (@jessphillips) June 11, 2020
The decision of the Sun to put an abusers ‘side of the story’ reflects how violence against women so often gets dismissed ‘as a domestic’ and so debate focuses on ‘reasons it happens’ rather than how to stop it. Heads should roll for doing this, not newspaper presses…— stellacreasy (@stellacreasy) June 12, 2020
The Sun’s headline quoting JK Rowling’s abusive ex-husband is beyond triggering for many abuse survivors, and enabling to abusers. It is irresponsible and dangerous. I could weep for the way women are treated by the tabloid press- still- in 2020.— Gillian Martin (@GillianMSP) June 11, 2020
The row about Rowling's comments on transgender issues began last weekend, after she responded to a headline on an online article discussing "people who menstruate" by writing in a tweet: "I'm sure there used to be a word for those people. Someone help me out. Wumben? Wimpund? Woomud?"
Harry Potter actor Rupert Grint is the latest star to voice his support for the trans community, following Rowling's comments.
His co-stars, Daniel Radcliffe and Emma Watson, are among others who have already spoken out.
In her blog defending her comments, Rowling said: "I've been in the public eye now for over 20 years and have never talked publicly about being a domestic abuse and sexual assault survivor."
She added: "I'm mentioning these things now not in an attempt to garner sympathy, but out of solidarity with the huge numbers of women who have histories like mine, who've been slurred as bigots for having concerns around single-sex spaces."