By bringing this question up, Calhoun was changing the way he would address Morganna and, more importantly, checking the leverage he had when it came to King Laurence.
King Laurence stared at Calhoun as well as his mother. Silence filled the room once again, and the King finally spoke,
"Even though all of us are aware of your relationship with the Queen, addressing her as your grandmother in here isn't right." Hearing his words, Queen Morganna smirked at Calhoun. "The royal court room is a place where important discussions and decisions are taken. But," he paused, gaining everyone's attention, "You can call her grandmother when you aren't in this room."
Morganna gritted her teeth as she couldn't go against the King's words, but it didn't mean she wouldn't bring this matter up when it was just her and her son alone.
Calhoun's smile widened, and he bowed once more, "I cannot tell how grateful I am to have a family here, my King."