It was brought up in the epilogue, im not sure how they found out. The dialogue was, during the wedding day prep, her friend asked her if that man, her dad, was going to come. Which she answers "No". The family hated him, how could she let that man come to her wedding.
Mentioning this person, they thought of Mo Ze. It was mention in this context:
---
Mo Ze was very special to Huo Wu. However, Huo Yusen was the won in the end, taking the beauty home.
In fact, Yu Xinxin didn't have much idea about who Huo Wu chose. In her view, as long as Huo Wu had a happy life. But now that the gate was open, she would gossip on the way, "Does Mo Ze now have a girlfriend?"
Huo Wu was stunned, and then nodded.
Yu Xinxin actually didn't think there was any accident. It's strange for someone like Mo Ze to have no girlfriend. She smiled and said, "His girlfriend must be pretty?"
Huo Wu this time, hesitated for a while before nodding.
Mo Ze's girlfriend is indeed very beautiful, but her girlfriend's appearance is similar to her. Especially the woman's eyebrows looked like her. She saw Mo Ze in the circle of friends and posted a photo with his girlfriend. She liked it and said congratulations.
At that time, he did not respond. Until Mo Cenfeng was known to be her biological father, he took the initiative to find her on WeChat and said that if it were not because of Mo Cenfeng's relationship, he would not let her go so easily. Until this time, Huo Wu did not know that Mo Ze actually did not let her go completely. His former girlfriends were all sexy with big assets, but his current girlfriend is very similar to her in appearance. They are well-proportioned and exquisite.
-----MTL only
That was it. It was only briefly mentioned how MP feels about finding they have the same father.
On MC's end, the Gu family hated him and so was MC.