Sister Monica Joan, played by Judy Parfitt, died from kidney disease.

Sister Monica Joan's death was sad for fans, but she will return. The show will have a prequel series with a younger Sister Monica Joan.

The prequel, Sister in Arms, is set in World War II in Poplar, London.

Sister Monica Joan died in the season 15 finale of Call the Midwife.

The prequel will have younger versions of Sister Monica Joan and other characters.

Three new young midwives will join the returning Sisters in the prequel.

The prequel is about strong women during World War II, says creator Heidi Thomas.

Heidi Thomas wanted to explore the past of the midwives in the prequel series.

The Blitz years in the East End were extraordinary, says Heidi Thomas.

Sister Monica Joan and Sister Julienne will return as younger characters.

There will not be a Christmas special of Call the Midwife this year.

Heidi Thomas said there will not be a traditional Christmas special this year.

The prequel, Sisters In Arms, will air during the Christmas period instead.

A Call the Midwife film is also planned, set in 1972, along with season 16.

Call the Midwife is available to stream on BBC iPlayer.