the extra hand

Ni Qing is laughing to see her husband childish behaviour to find out the truth about their past meeting. she actually exaggerates a little bit with the promise to marry the crown prince. The king actually already proposes to her on the spot, but Ni Qing already refuses the proposal. She informs them about her engagement with general Lin Yue. However, the king promises in future if their engagement and wedding fall out then Ni Qing has to accept the proposal from the crown prince.

It means there is a spy inside the Dayu Kingdom to inform everything about the ordeal of Ni Qing and Lin Yue. But their spy misses out on the fact about her marriage to the emperor of the Dayu Kingdom. They must be not competent enough to miss the most important information from the King.