Tom Felton, who played her son Draco, shared a touching tribute on Instagram.
He posted a picture from Harry Potter and the Deathly Hallows: Part 2 of himself holding hands with Helen. In the caption, he wrote, "So sad to say farewell so suddenly."
"I never took the chance to tell her but she helped shape me as a person so much — on- and offscreen," he continued.
"She was always relentlessly herself: razor-sharp wit, silver-tongued, kind, and warmhearted. She suffered no fools yet had time for everyone."
"Thank you for lighting the way forward and holding my hand when I needed it," he concluded.
Sending so much love and light to you, Tom. Wands up for Helen!