The Knight Captain is the New Princess-to-Be(2020)

Himegimi wa Kishi Danchou

Christina, a.k.a. “Lady Chris,” was born into a noble family and treated more or less like a boy growing up. Now a young woman, she’s not only captain of the imperial guards–she personally protects Prince Leonardo, who has been a dear friend since childhood. When Leo’s father, the king, demands that Leo find a suitable girl to marry, he says that he’s already found one: Chris! Chris is shocked, but figures that Leo doesn’t really love her like that; it’s probably just some ploy to keep his father happy. She decides to play along, but as the charade goes on, she starts to wonder if maybe her princely pal does see her as more than a friend.

(Source: Seven Seas Entertainment)