The series takes place in the 1950s, it follows the relationship between Princess Anilaphat (Anin) and Lady Pilantita (Pin), beginning in childhood.

By the age of 15, Princess Anin has to pursue her study in England resulting in her leaving her close friend, Lady Pin.

By the time she returns to her home country for her brother's engagement, Princess Anin does everything it takes to get close and confess her love to Lady Pin; however Lady Pin is arranged to be married to Master Kueakiat (Kuea).

On August 18, 2023, IdolFactory released character images of Armstrong and Chankimha and announced the project as the first Thai GL period drama.

On February 28, 2024, a Memorandum of Understanding (MoU) was signed by the Ministry of Commerce with IdolFactory with the aim to promote Thai goods and services to the international markets through their productions, including The Loyal Pin.