Are they siblings?

No. He is the son of the emperor, and she is the daughter of the empress and a foreign king.

Oops, I just saw your post date. It looks like you haven't read the recent chapters. That's when you find out.

I only saw it by chance on tiktok, so i don't know the story. They just look the same that's why i asked (●'◡'●)ﾉ