Derry Girls child star Zoe Brown has been diagnosed with leukaemia.The four-year-old played Baby Anna, the younger sister of Erin Quinn, in the Channel 4 show which is focused on the lives of teenagers growing up in Derry during the Troubles. She played the role alongside her twin sister Sophie and starred in the second and third series of the show. Zoe was diagnosed with leukaemia in May and has been undergoing treatment and chemotherapy.