Prince no Koi

Mandy lives a peaceful life with her parents and her adopted son Josh, the child of her best friend who died 3 years ago. However her quiet life is jeopardized when a man suddenly visits her. This refined and dignified man is the 2nd prince of Castile, Prince Stephen! Josh's father, who was the crown prince of the Kingdom of Castile had passed away, and the prince claims Josh is the rightful heir to the throne. "I'll never hand over my son!" Standing by her promise to her friend, Mandy decides to do everything in her power to stop the prince.
Source: mangaupdates