Tributes have been paid to Nanny McPhee star Raphael Coleman following his death at the age of 25.

The former child actor and climate activist died after collapsing having had no previous health problems, according to his stepfather.

In a Facebook post, Carsten Jensen described his stepson when he was younger as “a little redhead boy who was always mixing explosive chemical ingredients”.

Mr Jensen added: “He had several roles, was rewarded and could have chosen a career as an actor. But he wanted to be a scientist, not to blow up something, as his figure in Nanny Mcphee, but to save the planet.”

The Facebook post, called “To die young”, was accompanied with a picture of Coleman at a climate rally.

Mr Jensen said Coleman had “collapsed without prior health problems in the middle of a trip and could not be restored”.

“I guess there’s nothing that makes you see death as unfair and meaningless as when a young person dies. It’s life itself that’s sabotaged,” he added.

Coleman’s mother Liz Jensen tweeted a video of her son and said that he “loved life so much”, adding he was a “courageous spirit”.

Coleman studied wildlife conservation before he joined climate group Extinction Rebellion, under the name Iggy Fox, where he made digital content and ran social media accounts.

He was arrested several times during his work with the group – including outside the Brazilian Embassy in August as well as in October in Trafalgar Square.

Writing on the organisation’s website last year, he said: “I don’t want to go to prison, but I’ll face whatever I need to. My actions aren’t about sacrifice, or arrest for the sake of it.

“Knowing the science, I have no choice but to tell the truth, and stick to my morals in the face of that truth. I won’t stand by and watch the world burn.”

Extinction Rebellion tweeted: “He was 25, had given up a career in science to join XR and fought hard for the cause, especially for Indigenous rights.

“Iggy will be deeply missed by us all.”