As one of the Khan's many descendants, Tuo Sai wouldn't be surprised if his grandfather didn't know him at all if nothing had happened.
His father, King Riyao, was ranked seventh for succeeding the throne, though it was said that the seventh king had never inherited the title of Khan in all of Norland's history. There were exceptions of lower-ranked kings becoming the Khan, such as the eighth, ninth, and tenth kings, but the seventh king had never succeeded the position of Khan. King Riyao had tried to break the cycle but was soon defeated. After years of observation, he went down the same path as all the previous seventh kings, which was to support a more promising king.
Tuo Sai had always followed his father's orders, so he had naturally joined King Kuari's side. He had even become friends with King Kuari's younger brother Kuo Zhen even before his father openly stated his stance.