Game of Thrones Season 6 Episode 10 The Winds of Winter
Tommen, who had been forcefully restrained to his quarters, witnesses the explosion and, realizing that his mother is responsible, commits suicide by throwing himself from the top of the Red Keep. When Qyburn asks Cersei what to do with his body, Cersei coldly replies that his remains are to be burned and the ashes buried at the ruins of the Great Sept.
QYBURN: What are your thoughts concerning the king’s funeral? As the Sept of Baelor is no longer an option, perhaps a ceremony in the throne room?
CERSEI: He should be with his grandfather, his brother, his sister. Burn him and bury his ashes where the sept once stood.
Source text: Wikipedia.