Vin Diesel struggled to work following Paul Walker's death.

The 46-year-actor found it ''challenging'' to return to the set of his new movie 'Guardians of the Galaxy' following his 'Fast and Furious' co-star's death last November.

Diesel put his energy into his work and focussed on his portrayal of Groot, who he lends his voice to in the sci-fi-adventure, and found this ''therapeutic''.

During a Facebook Q&A on Monday (19.05.14), he said: ''It was very personal- it was the month after the accident happened with my brother Paul Walker and it was the first time I had worked since.

''Although it was challenging, just to get back to work was therapeutic- especially as Groot. There was an innocence about the character that was just refreshing- and it may have been more challenging under other circumstances, but at that time, it was very therapeutic.''

Walker - who starred alongside Vin for over a decade in the 'Fast and Furious' movie franchise - died along with his friend Roger Rodas on November 30 after the Porsche Carrera GT they were travelling in crashed into a tree and burst into flames in California.

The coroner listed speed as the lone reason for the fatal crash after investigators found no sign of mechanical fault.