HUGE SPOILER

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.So he really became pregnant after having a deed with the prince. It became successful since the prince has a dragon blood in him (?) *note: i think the prince doesn't know that the Duke's having sex with him since he was totally out of himself, the duke make him drink a potion (i guess?)
also both of them has an item wc they can alter their looks but eventually the duke knows it was the prince since he pulled out his earring (the item) while having sex with him wc revealed himself.

Then the prince has a dream of two headed golden dragon wc the duke gave birth to- a twin little version of him.

The prince doesn't even know that he has a vagina and doing the deed with men so when he truly misses him he eventually go where the duke castle is and end up in the garden wc the duke, the butler and the beast are having a threesome that day. In the end he explain and so he found out that he's pregnant with him (?)

Also it became a harem since the butler, the beast slave and the prince both enticed with him and they are always horny especially the duke and always end up in foursome.

Additional, the duke is really strong since he doesn't even know that he will giving birth. He even had a threesome in the morning, go in a hike (?) and fought monsters (ogre) that day and after he came home his birth water broke. But both the twins are healthy.

*This is from my understanding. But overall it was worthy to read especially the art is giving. Full of porny stuff lol.