Lah Ruk Sut Kob Fah

Both:
- bodyguard that falls in love with royalty
- forbidden love
- duty over love
- cute main couple
- takes the leads a while to finally become a couple
- female lead is being forced to marry a prince

Both are about being part of a modern royal family, about living in the palace and about royal guards. Both have romance, comedy, action and politics.
In both dramas the girl is choosen to marry a prince from another country. In King2Hearts it's a marriage between North and South Korea. In Lah Ruk Sut Kob Fah a girl from Thailand is about to marry the prince of Raya.

Same royal setting
Different trope with male lead as bodyguard
Not as lighthearted as princess hours