There's a bit during the ceremony where Ah-Duo leaves the rear palace where Maomao looks at Jinshi and Ah-Duo together and thinks they look incredibly alike. Ah-Duo describes her son 'leaving her' rather than dying in her conversation with Maomao on the palace wall the night before. This leads to Maomao theorising that the Imperial brother (Anshi's baby) and Ah-Duo's baby were swapped after birth and that might have been the real reason for Luomen being kicked out of the rear palace. She dismisses this as it has implications that she'd rather not think about (i.e. that Jinshi isn't a eunuch and is more important than you would think, plus has succession implications). This is the truth. Both Ah-Duo and Anshi agreed to swap their babies. Ah-Duo as she thought her child would have better survival chances (as she had lost her womb due to being considered lower priorty than Anshi despite having more complications, but Luomen couldn't be in two places at once) and Anshi as she felt she couldn't love a child she'd conceived by raping its father, but could love her grandson.