Complex sentence: In September 2015, Netflix purchased the programme, commissioning a series of 12 episodes later divided into two series of six episodes; the fourth series was released on 29 December 2017.
Split into simpler sentences: In September 2015, Netflix purchased the programme, initially commissioning 12 episodes, later divided into two series of six episodes. A fourth series, also with six episodes, was released on 29 December 2017.