Animation in black and white are featured in the documentary World War II: China's Forgotten War. [Photo provided to China Daily]

"We opened the film in this way because we wanted to show that when the mass murders took place in Poland, a similar incident on a bigger scale had already taken place on the other side of the world."

China Intercontinental Communication Center, which has previously done co-productions with the BBC, the National Geographic Channel and Arte, the French-German TV network, decided to make the film after Spring Festival in 2014.

They recruited Singapore-based InFocus Asia as the production company and had lengthy discussions as to whether to have a host presenter.

"Most documentaries like this do not have a host," says Peter Chen, the 36-year-old head of co-production at CICC.

"When we planned the documentary we were unaware of Rana's book, which was only published in Chinese last year. People who are good at writing books are not always the right host for a TV show."

Mitter, although not a TV presenter, does host a radio show called Free Thinking on BBC Radio 3 in the UK.