Some 700 children are set to perform at the Royal Albert Hall in the Music for Youth Proms on Tuesday evening.
Among them are singers from north London who will perform a powerful piece of music exploring gang violence and culture in Newham.
Ali, 15, told the Victoria Derbyshire programme how he overcame his initial nerves.
Watch the Victoria Derbyshire programme on BBC Two and BBC News Channel, 10:00 to 11:00 GMT – and see more of our stories here.
