I Don't Know That Your Majesty Is a Girl

The new emperor, Qi Nian, acceded to the throne many years ago. He kept refusing the requests by his officials to choose a consort, brushing them off by saying "I am busy with work. The affairs of state are more important." But Qi Nian finally relented as rumors that "the emperor is impotent" began to spread.

Yu Dingdang is a rather dim-witted girl, but born to a prestigious family. This led many to say: "Miss Yu exchanged her brain for her looks". Nobody expected that she would be chosen by the emperor to be his empress consort? Yu Dingdang acted surprised on the outside, "Who? What? Me?" But inside she was thrilled, because she has wanted to become Qi Nian's bride ever since she was little. When she successfully marries her crush, that is when a slapstick comedy breaks out in the palace, when she finds out that the haughty emperor is actually a woman?!

(Source: Bilibili, translated)