Himitsu No Himegimi Uwasa No Ouji

From Aerandria Scans:
Roochen and Galnia are two countries that have been at war with each other for a long time. Now that peace has been established, princess Aldina of Roochen has to marry the prince of Galnia. However, according to the rumors, the prince of Galnia is a total debauch, and he does nothing but playing around?! Aldina wants to see for herself who the prince really is, so she disguised herself as a boy and tried to approach the prince…