Or maybe not. Who knows ┑(￣Д ￣)┍
as for as i remembered in the ewrly chapter Yi Yun got the parental tests anf it showed that Feng Feng is the real father so basically he knew already. It did not tackled much after that. Yi Yun just accept the fact and weighed things if Rourou will ever choose him despite he doesn't have anything compared to Feng feng.
i think he knows when he did the dna test awhile ago. then it showed he tore up and threw away the results and he was freaking out for awhile about how if feng feng decided to take rourou away from him, he'd never win in court. so he never brought up the biological parent issue again and they ended up not properly talking about it. and it became less concerning as they got closer and feng feng kept promising to raise rourou together.
Omg it really did happen xD
How can I forget that HAHAHA
I think the real drama will start if Yi Yun found out that Rourou's not his legitimate child. Or is it already out? Sorry, I forgot xD But yeah, that's just my personal opinion ٩(๑❛ᴗ❛๑)۶