Harry Potter star Daniel Radcliffe has waded into the transgender row involving author JK Rowling and said he hopes her comments will not "taint" the series for fans.
Rowling attracted criticism for tweets posted over the weekend.
She took issue with a headline on an online article discussing "people who menstruate," and said: "I'm sure there used to be a word for those people. Someone help me out. Wumben? Wimpund? Woomud?"
Critics accused her of being transphobic, an allegation Rowling strongly denies.
Actor Radcliffe, who became a worldwide star after playing schoolboy wizard Harry in the blockbuster adaptations of the beloved book series, has now commented on the controversy, stating "transgender women are women".
He shared a statement through the LGBT suicide prevention charity The Trevor Project, saying that while Rowling "is unquestionably responsible for the course my life has taken… as a human being, I feel compelled to say something at this moment".
Writing that the issue is not about "in-fighting between JK Rowling and myself," Radcliffe said: "Transgender women are women. Any statement to the contrary erases the identity and dignity of transgender people and goes against all advice given by professional health care associations who have far more expertise on this subject matter than either Jo or I."
The 30-year-old then cited statistics from The Trevor Project, claiming 78% of transgender and non-binary youth reported being the subject of discrimination due to their gender identity.
He said: "It's clear that we need to do more to support transgender and non-binary people, not invalidate their identities, and not cause further harm."
And Radcliffe addressed fans on social media who said they could no longer enjoy the Harry Potter series due to their disagreement with Rowling.
"To all the people who now feel that their experience of the books has been tarnished or diminished, I am deeply sorry for the pain these comments have caused you," he said.
"I really hope that you don't entirely lose what was valuable in these stories to you. If these books taught you that love is the strongest force in the universe, capable of overcoming anything; if they taught you that strength is found in diversity, and that dogmatic ideas of pureness lead to the oppression of vulnerable groups; if you believe that a particular character is trans, non-binary, or gender fluid, or that they are gay or bisexual; if you found anything in these stories that resonated with you and helped you at any time in your life — then that is between you and the book that you read, and it is sacred.
"And in my opinion nobody can touch that. It means to you what it means to you and I hope that these comments will not taint that too much."
Following a backlash, Rowling, 54, stood by her comments, arguing "it isn't hate to speak the truth".
She tweeted: "If sex isn't real, there's no same-sex attraction. If sex isn't real, the lived reality of women globally is erased. I know and love trans people, but erasing the concept of sex removes the ability of many to meaningfully discuss their lives. It isn't hate to speak the truth."
It is not the first time Rowling has been accused of being transphobic. In December she voiced her support for a researcher who was sacked after tweeting that transgender people cannot change their biological sex.