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This weekend at Letters Live, a U.K. event at which celebrities like Benedict Cumberbatch and Carey Mulligan read letters aloud in celebration of “literary correspondence,” one message in particular stood out. Actress Ellie Bamber chose to read an open letter to J.K. Rowling from a woman named Chrissy Hart. Hart’s daughter had recently passed away from cancer, and she wanted to thank Rowling for the way the Harry Potter books helped her family cope throughout the sickness.

“You taught her that for every chemo she has to go through, there will be the opportunity to fly across a lake on a hippogriff,” Hart wrote. “For every time her heart seizes with fear of pain, there will be me chasing it away with a patronus charm. Your words built a castle for her to move into when the prognosis got worse. Mrs Rowling, cancer threatened to take everything from my daughter, and your books turned out to be the fortress we so desperately needed to hide in.”

The beautiful letter was quickly circulated by fans; Star Wars actress Daisy Ridley even shared it on Instagram. On Monday, Rowling responded to the letter on Twitter. She said that words were always her safe place, and expressed bittersweet empathy with Hart.

Read the full letter here, via BBC News.