“Transgender women are women,” the actor said in a Trevor Project blog post Monday. The organization offers crisis intervention and suicide prevention services to LGBTQ youth. “It’s clear that we need to do more to support transgender and nonbinary people, not invalidate their identities, and not cause further harm.”

Radcliffe’s post went up two days after Rowling’s series of tweets, which started with a link to an opinion piece titled, “Creating a more equal post-COVID-19 world for people who menstruate.” While posting the link, Rowling tweeted: “‘People who menstruate.’ I’m sure there used to be a word for those people. Someone help me out. Wumben? Wimpund? Woomud?”

When Twitter users said her comment was “anti-trans” and “transphobic,” Rowling doubled down, tweeting: “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.”

As criticism of Rowling’s remarks grew, LGBTQ rights group GLAAD also took to Twitter, saying, “JK Rowling continues to align herself with an ideology which willfully distorts facts about gender identity and people who are trans. In 2020, there is no excuse for targeting trans people.”

“According to The Trevor Project, 78% of transgender and nonbinary youth reported being the subject of discrimination due to their gender identity,” Radcliffe said in his post. He also said he himself had much to learn, while encouraging the public to educate itself “about transgender and nonbinary identities.”

Radcliffe—who starred as Potter in eight films based on the book series—isn’t the only actor from the films to throw his support behind the transgender community. Katie Leung, who played Cho Chang, posted links to organizations supporting black transgender people.

Meanwhile, Radcliffe also acknowledged the impact Rowling has had on his own life, while saying he was sorry for Harry Potter fans who felt Rowling’s comments “tarnished or diminished” their love of the series.

“I really hope that you don’t entirely lose what was valuable in these stories to you,” he said. “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.”