The Lost Prince is a British television drama about the life of Prince John – youngest child of Britain's King George V and Queen Mary – who died at the age of 13 in 1919. John had epileptic seizures and an autism-like developmental disorder, and the Royal Family tried to shelter him from public view; the script did not present the Royal Family as unsympathetic, instead showing how much this cost them emotionally. Poliakoff explores the story of John, his relationship with his family and brother Prince George, the political events going on at the time and the love and devotion of his nanny, Charlotte Bill (Lalla).

Prince John was the fifth son and youngest of the six children of King George V and Queen Mary. At the time of his birth, his father was heir apparent to John's grandfather Edward VII. In 1910, John's father succeeded to the throne upon Edward VII's death, and John became fifth in the line of succession to the British throne.