The Crown star said she was “incredibly proud” of the the young actor, who plays Nick Nelson in the teen Netflix drama, after he shared that he is bisexual in October.
In a post on Twitter, Kit admitted it was something he felt he’d been “forced” into doing.
“Back for a minute,” he tweeted. “I’m bi. Congrats for forcing an 18 year old to out himself. I think some of you missed the point of the show. Bye.”
Speaking about her co-star, Olivia – who played Kit’s mum in the Heartstopper – has now told Variety: “I am so proud of him, but I am not proud of how people bullied him.
“I think people should be allowed to have their own journey,” she continued. “But I’m incredibly proud of him as a young man to deal with all of that and be in the spotlight. It’s unfair. But he’s amazing. He’s a very beautiful human being.”
After Kit’s post, Heartstopper’s showrunner Alice Oseman was among the first to voice their support and condemn those who “gleefully spend their time speculating about sexualities”.
“I truly don’t understand how people can watch Heartstopper and then gleefully spend their time speculating about sexualities and judging based on stereotypes,” they wrote.
“I hope all those people are embarrassed as F*CK. Kit you are amazing.”
In May, Kit explained why he’d chosen not to label his sexuality when he appeared on the Reign With Josh Smith podcast.
“I just think that there’s a danger with things on social media,” he said.
“In the cast, we’re all young – I’m 18 – and we have a few people in their early twenties as well and to start speculating about our sexualities and maybe pressuring us to come out when maybe we’re not ready.”
He added: “I mean, for me, I just feel like I’m perfectly confident and comfortable in my sexuality, but I’m not too big on labels and things like that.
“I’m not massive about that. And I don’t feel like I need to label myself, especially not publicly.”