Benedict Cumberbatch said his mother was in tears when he got the audience at the Wilderness Festival to sing Happy Birthday to her.
The Sherlock star, 41, was one of several celebrities who took part in the event in Oxfordshire, delivering a performance of Letters Live, which sees people reading monologues based on real correspondence.
After the crowd sang Happy Birthday to fellow performer Mark Strong, Cumberbatch asked them to sing to his mother, Wanda, too.
He told Jo Whiley on BBC Radio 2: “They sang a rousing videoed message to my mum so I think I got some points there!”
Asked about her response, he said: “I think the words in the email from dad were something like, she was suitably overwhelmed and questions why it’s possible that I continually make her cry.”