Love in the Moonlight

In 1963, following political change in Sariangkham, Prince Saenkaew of Nanta is sent to Bangkok to marry Pinanong—a union that would help transfer the family's assets to Thailand. It isn't an unfavourable match to Pinanong who's had a crush on the prince since childhood. Her older brother Sasin, however, is suspicious of the arrangement. He's fond of teasing the prince, and as Saenkaew opens up about his feelings having to marry as his duty to his family, the two grow close, their connection deepening into something altogether unexpected.

(Source: MyDramaList)