“Yellowstone” star Cole Hauser paid tribute to his late mother, announcing her passing on Thursday, with an Instagram post featuring a photo of them posing next to each other on horseback while on the set of the show. “It is with a heavy heart that my mother Cass Sperling Warner passed away at the age of 76. Her kindness, love, humor and amazing spirit will be missed by not only my family but the world,” Hauser wrote in the caption. “You have touched so many. I know you will be up in the heavens sitting next to all the great humans that have passed through our earth. We will meet again. Bye for now,” he continued.