The Chocolat author Joanne Harris has said that she thought of her cancer as a fictional “monster” while she was having treatment, so that she “could destroy him”.

The writer, who was diagnosed with breast cancer in 2020, shared her experiences with her followers on social media, dubbing her illness “Mr C”.

“I turned him into a character so that I could destroy him,” she said in an event at the Hay festival. “Because that’s what I do.”

After three rounds of chemotherapy, “slightly numb toes” is now the only symptom she is now experiencing. “I think that’s a small price to pay for killing off Mr C,” she joked.

Harris, who is chair of the Society of Authors, said she chose to be so open about her illness online because of the “sense of community” websites such as Twitter offer. She said she missed the way she had been able to chat with colleagues in her former career as a teacher. “Social media kind of filled that gap and became my staff room, if you like,” she said.

With that openness came unexpected rewards too: “I didn’t realise how important it might be to certain people,” she said, explaining how social media users had got in contact to say that her posts had reminded them to make their mammogram appointments – as her cancer was discovered from a routine examination.

Through posting about Mr C, the writer was able to get in contact with others who had been through the same treatments she was going through. “And it also gave me something to get right,” she said, describing how she would think to herself: “You’re not going to just sit and cry at home today. Because you know what, Twitter is counting on you, you really need to tell them a story.”

Sharing her writing online throughout the process “energised” her, she said.

Harris, who considers herself gender fluid and uses she and they pronouns, has also previously used Twitter to show her support for transgender rights. When asked during the Hay event about the inclusion of a trans teenager, Ben, in her most recent novel A Narrow Door, she said “trans kids exist and should be represented”, adding that the character “almost wrote themselves” because it was so obvious to her that Ben was going to be trans when she was writing the book.