Toward the end of season 4, Grimm infamously killed off Nick’s mother, Kelly (Mary Elizabeth Mastrantonio), off-screen. Here’s why that happened.
A gruesome scene in Grimm season 4 revealed that the NBC series had killed off Nick’s mother off-screen. Played by Mary Elizabeth Mastrantonio, Kelly Burkhardt was a recurring character who first appeared in the Grimm season 1 finale. For years, Nick wrongly believed that both of his parents were dead, and was shocked to discover that she, a Grimm, faked her death. After their reunion, Kelly returned to Portland briefly in season 3, and appeared in the Grimm series finale as a ghost.
Kelly never appeared in-person in Grimm season 4, but was mentioned often, particularly in the storyline related to Juliette (Bitsie Tulloch) and her transformation into a villain. At the time, she was exchanging emails with Juliette, unaware that she was being led into a trap. In the penultimate episode of Grimm season 4, Kelly (clearly played by a stand-in, as her face was never shown) walked into the house and was ambushed by minions of the season 4 villains, the Royals. In the final scene of the episode, Nick (David Giuntoli) found a small box and opened it up to gaze down at Kelly’s severed head.
Why did Grimm kill off Kelly, and why did it happen in such a horrific manner? Grimm co-creators David Greenwalt and Brian Kouf explained in an interview that they wanted Mary Elizabeth Mastrantonio back on the show, but scheduling conflicts got in the way. At this time, Mastrantonio was filming the pilot for a different CBS series, Limitless. But, Greenwalt and Kouf agreed that not actually using the actress and having the death take place off-screen was the “right story move” for the show. Also, they said that it seemed “more interesting” to hear the fight rather than see it, and to watch Juliette’s face as she witnessed the consequences of her actions [via TVLine].
Fans were upset by the way that Grimm killed off Nick’s mother. Admittedly, Nick finding her head in a box was a rather unceremonious exit for a character who was well-liked by viewers. Many people felt that a different way could have been found to write off the character – if that was what needed happen – but it should be pointed out that how her death was handled was important to both the ending of Grimm season 4 and Nick’s season 5 story.
The utter shock of seeing his mother’s head had a traumatic effect on Nick, and it helped push him in the direction that he needed to go. Even though it was easy to guess what was inside the box, it created a suspenseful moment, as viewers had to wait to see Nick’s reaction. Anger over what happened to his mother led Nick on a mission of revenge, and it even made him willing to come to blows with Juliette, who had been his primary love interest for four seasons. Now while he was unable to kill her, he didn’t hesitate to kill the Royals. Kelly’s murder and Juliette’s death at the hands of Trubel (Jacqueline Toboni) fit the season’s dark tone and put Nick in a position where he felt that he had lost everything.