Couple of Four Generations

She was his crown princess, but once he ascended the throne, she was only a concubine. She was his first wife, he eventually became a subject, but she was abandoned. She was his half-sister. He sacrificed his life to save her, but she married his enemy. She is his little apprentice. Although he has no desires, she is the only one favored. "Master, you said we were in love for the fourth generation?" "Yes, love has finally been achieved in the fourth life."