Grand Master Knight Has Become the Princess

Himegimi wa Kishi Danchou / 姫君は騎士団長 on treemanga.com

Christina, a girl raised like a boy, is the grand master knight of the guards assigned to Prince Leonardo of the kingdom of Lobolovsky, as well as the prince’s friend. One day, the prince asks her to pretend to be his betrothed for the sake of the country, to which she reluctantly agrees. This is the story of the kingdom’s strongest warrior getting used to life as a princess!