Shounen Oujo

In a country where women rule supreme lives a poor but happy boy named Albert. An excursion to the city turns dangerous when he and his friend are abducted by slave traders, and later purchased by a noblewoman's servant. If this wasn't crazy enough, it turns out Albert looks exactly like the noblewoman who purchased him. But she's no ordinary aristocrat. She's a princess! And he's to act as her double from today on!?

(Source: Comic Sylph)