Overnight Husband.

Chonpansa got pregnant with her son, Luk Prun, after a one night stand with an unknown man who she later suspected to be Chayut, the half-brother of Kasak. With that suspicion, Chonpansa goes out of her way to treat Chayut well, causing a misunderstanding for Kasak and making him think she's trying to get with his brother in order to promote her position. In trying to save his brother, Kasak took actions and announce his fake romantic relationship with Chonpansa, making her and Luk Prun move in with him.