The series ends with Cassie and Sunny bringing flowers to Hayley’s final resting place at a memorial garden.
The hit crime drama Unforgotten returns to ITV on Monday 22 February at 9pm for its fourth series, with Cassie and Sunny back on the scene to crack some more cold cases.
The drama focuses on the murder cases rather than any personality quirks the pair may have and their relationship is platonic.
The show, which debuted in 2015, is written by Chris Lang, who also wrote Dark Heart and The Hookup Plan.