Jason Isaacs has shared a funny tribute to his Harry Potter co-star and “favourite son” Tom Felton to celebrate his 31st birthday.

Isaacs played villain Lucius Malfoy in the hit film series, while Felton played his son Draco, Harry’s main nemesis at Hogwarts School of Witchcraft and Wizardry.

Isaacs tweeted: “Happy Birthday to my favourite son.

“You’ve brought the Malfoy name into horrendous disrepute by turning out to be a gorgeous human being and a fairly average guitarist. I’m so ashamed and proud of you.”

Referring to Draco’s famous crop of bright blond hair, which is at odds with Felton’s own dark locks, Isaacs added the hashtag: “#BrunettesHaveMoreFun.”

The 55-year-old actor also wrote “LuvYa”, while sharing a picture of himself and Felton hugging, and another of Felton as a young actor at the start of the Harry Potter series.

Felton starred alongside lead actors Daniel Radcliffe, Emma Watson and Rupert Grint in the film series based on JK Rowling’s novels about the boy wizard from 2001 until 2011.

He has also appeared in films including Rise Of The Planet Of The Apes, Belle and A United Kingdom, and has released a handful of EPs and singles as a singer-songwriter and guitarist.