Royal Daughter in-law(2015)

Royal Daughter in-law is a Thai drama following Khunchai Rong, a nobleman forced into an arranged marriage with Srijittra, the dutiful elder daughter of the Rachadamri family. Rong resists the union, already in love with the divorced Khunying Koy, but his family forbids the match. Srijittra accepts her fate and moves to the palace to learn royal etiquette, only to be ignored by her new husband, who continues his affair with Koy. When Srijittra's spirited younger sister Salin visits and discovers Rong's infidelity, she vows to free her sister from the loveless marriage. As Salin schemes to help Srijittra, unexpected twists draw her and Rong closer together, sparking an unlikely romance that threatens to unravel the family's carefully laid plans.