‘Yellowstone’ actor Cole Hauser is mourning the death of his mum. The 48-year-old star, best known for playing Rip Wheeler in the Western drama, announced the news of Cass Warner’s passing by sharing a photo of her on Instagram that showed them riding horses together. He captioned the image: “It is with a heavy heart that my mother Cass Sperling Warner passed away at the age of 76. “Her kindness, love, humour and amazing spirit will be missed by not only my family but the world. You have touched so many.” He added: “I know you will be up in the heavens sitting next to all the great humans that…