When does All Creatures Great and Small return?

The title aired over seven series, totalling 90 episodes, from 1978 to 1990. Set in the Yorkshire Dales and beginning in the mid-1930s, it stars Christopher Timothy as Herriot, Robert Hardy as Siegfried Farnon and Tristan Farnon. Herriot's wife, Helen, was initially played by Carol Drinkwater and Lynda Bellingham.