The aunt paid a surrogate maybe?
Probably a surrogate mother he met overseas
Personally, I like it believe it's the egg of the same woman that gave birth to Rourou.
but feng said "embryo"
Yeah, that means it's been fertilized this whole time, that would make it around the same time Rourou was conceived.
So maybe their age gap is likely 1 year apart right?
Who’s egg was fertilize with Yi’s sperm????