Shangguan Qing took his mother's surname, much like a child born from a woman who has called a man into marriage. Hence, he's not regarded as the sovereign's grandson by marriage, nor is he to be referred to as the sovereign's maternal grandfather, but rather as the Imperial Ancestral Grandfather.
However, at this moment, Xiao Hen would not easily call out this term "Imperial Ancestral Grandfather."
Based on the sovereign's attitude towards him, Xiao Hen had made a preliminary judgment about the status of the sovereign's eldest grandson in the sovereign's heart—the sovereign did care about this eldest grandson, even more than Xiao Hen had imagined.
Xiao Hen's decision was actually quite risky; if the sovereign didn't care for Shangguan Qing at all, then Xiao Hen would have needlessly exposed himself.
In the two bedchambers lay two people, one was Shangguan Yun who had just had surgery and was still unconscious, and the other was Gu Jiao, who had fallen asleep from exhaustion.
