Word to the wise: this is not an “m/m fantasy romance”. It’s m/m, and it’s fantasy, but mostly it’s … slavery harem smut? I don’t even know. Wouldn’t have thought twice if this had been on AO3, but billed as fantasy, the lack of any serious reflection on the horrors or downsides of slavery, rape and oppression is a bit stunning. I’m guessing this is like a small-scale Fifty Shades thing, where people enjoy the horny parts and forget to also use their brain when later recommending the story to people.
Anyways, prince gets backstabbed by his younger brother and ends up an anonymous sex slave to the enemy, in a culture where sex slaves are normal (they are normal in both countries, but there are subtle and uninteresting differences). It’s thankfully not quite enemies-to-lovers, but it’s obviously itching to get there.