Nanny McPhee star Raphael Coleman has died at the age 25.
Coleman, known as Iggy Fox, later became involved in climate activism and has been described as a "true warrior" for his work.
In a statement posted on Twitter on 7 February, his mother Liz Jensen, said her son had "died doing what he loved".
His stepfather, Carsten Jensen, wrote on Twitter that Coleman had "collapsed" while on a trip and said he had no prior health problems.
As a young actor, Coleman played the role of Eric in the 2005 family comedy Nanny McPhee, starring Emma Thompson and Colin Firth.
His co-star from the film Eliza Bennett said she was "heartbroken" by the news of his death.
She added: "He dedicated his life to protecting wildlife and fighting climate change."
After his early acting career, Coleman went on to work with the climate crisis group Extinction Rebellion.
In a statement on their website, the group wrote: "Iggy Fox, you will be missed and remembered. It has been an honour and a privilege to have known you, even if it was all too brief."
It added: "Iggy died as he lived: trying to make the world a better place, training to stop poachers in Africa and surrounded by trees and people who cared about him."
On his website, the Londoner described himself as "a twenty-something Zoology graduate travelling the world on a shoestring budget, working with wildlife and exploring wildernesses."
The 25-year-old helped to found and develop the Wildlife Workers' Network, a group working to document the work of "frontline nature guardians".