It is too late anyway

You don't become king by not being cognizant of your actions. Fornication would always carry the risk of illegitimate pregnancy and birth, despite the possibility of coitus interruptus where you pull out before ejaculation. However, despite the risk, both of you still do it.

The reason is simple, the two of you are getting high with thrill from the risk of inbreeding. But that's only a fantasy on both of your part. But what will happen if you're really following through your lust and instinct, and because of that, you impregnate your mother? Strangely, you feel that idea isn't repulsive. In fact, it excites you more as your dick become harder and your thrusting into your mother becomes faster and more intense. More and more the tip of your dick touches the back of your mother pussy as you and your mother abandon yourself to the waiting wreath of pleasure.

The two of you moan together when your cock start to pulse your seeds into her waiting womb. After your dick shrivels out of her, you lie next to her and the two of you enjoy the relief brought by your sexual activity. The two of you lay like this for a long time before your mother tries to get up. "I need to return to my room."

You pull her back to the bed. "Why?"

"But what will the people say if they see me leaving your room tomorrow morning?"

"Not as acute as their comment will be when you're pregnant despite being a widow. They will wonder who the father is."

"It is not guaranteed. After all, I can douche to reduce the risk even further."

You chuckle. "It seems that the multiple orgasms you experienced just now have returned sanity to you. But sadly, that's not to be."

"What do you mean?" your mother says while turning at you with an expression of panic.

Lying on your side facing your mother, you rest your head on your palm. "You know that it's too late, mother. We have sinned, and our sin will grow inside your womb, mother, even as you will nourish it with your motherly love. Even from then, until you give birth to it and throughout its life, our child will be the witness to our sinful incestual union."

"You're telling me as if you're not involved, son!"

You grin at that insinuation. "Oh, of course, I'm involved. When you come here in the middle of the night to offer yourself, I'm not exactly rejecting you. In fact, I'm very much involved just now. But, still, you're the one who comes to me."

"Yes, despite being a queen, in private, I'm just a wench who couldn't keep away from her son's bastard maker."

"Of course you are one."

Your mother huffs angrily. "And how about you, O' virtuous king?"

"Me?" you ask rhetorically while pointing at yourself. "I'm a humble motherfucker who's going to sire bastards with her majesty the former queen."

"It seems that upon ascending the throne, you've become more egoistic..." your mother trails. "Wait. Bastards?"

You get on top of your mother and kiss her, while your hand maneuveres your hardening dick into her wet pussy. You break your kiss for a moment to answer her question. "Yes. Bastards." You then restart your incestual intercourse with your mother, eager to increase the chance of her conceiving your child.