Come to that, how little attention does that douchebag king pay to his wife that he never noticed she's THAT pregnant lol
Well the King is apparently Infertile, meaning he has practically no reason to visit or get visited by any Women (including the Queen).
Also, in the olden days, King & Queen used to sleep in different rooms, and when the King felt having sex with the Queen, he either visited her room or called her to his room.
There also seems to be the fact that, the Queen doesn't have much Court Power, meaning her public appearance is much rare as well (she can appear or not appear whenever she wanted, and no one questioned it, so staying away from public eye including the King for a few months isn't that surprising).