Marshals surprised viewers by killing off Kayce Dutton's wife, Monica, which will continue to play out in the Yellowstone spinoff. After the Sunday, March 1, series premiere, confirmed that Kelsey Asbille wasn't coming back to reprise her role, Marshals star Ash Santos weighed in on how Monica will remain at the center of the story. "The entire season is shaped by - at least for Kayce - his grief and it ends up affecting all the characters in a different way," Santos exclusively told Us Weekly. "Because some of us on the show already knew him, some of us didn't.