When Anton Yelchin died suddenly Saturday night in a car-related accident, he was still recording the voice for the lead character in the upcoming Netflix animated family event series Trollhunters from creator and executive producer Guillermo del Toro and DreamWorks Animation. While the project was officially unveiled by del Toro last week at the Annecy Animation Festival in Annecy, France, the series already had been in production and I hear Yelchin had completed a great majority of the episodes.

Trollhunters 2Because Yelchin’s passing was so unexpected, Netflix and DreamWorks Animation are yet to make plans how to address it, possibly casting a new actor for the remaining episodes. “Our hearts are heavy with this tragic news and Anton’s family and friends are in our thoughts,” the two companies said in a joint statement Sunday.

In heartfelt tweets, del Toro shed light on how long Yelchin had been working on the series. “The sweetest, most humble, delightful, talented guy you’d ever meet. Worked together for about a year. Shocked,” del Toro wrote Sunday, adding “Anton was a sweetheart. Absolutely a great creative partner and artist.”

Yelchin co-starred alongside Kelsey Grammer and Ron Perlman in Trollhunters, set to premiere in December 2016. The series features a tale of two fantastical worlds set to collide in an epic saga. Set in the fictional suburb of Arcadia, our unlikely hero, Jim (Yelchin), and his two best friends make a startling discovery that beneath their hometown lies a hidden battle between good trolls and bad, the outcome of which will impact their lives forever.

Yelchin’s Jim is an ordinary teenage boy whose discovery of a mystical amulet sets his life on a course filled with high-stakes adventure.