If you're hesitating about telling Hadrian Sanon about her father in Starfield, you're right to be, as it's a crucial choice in continuing the UC Vanguard faction questline. As you uncover the truth about Hadrian's father, aka Vae Victis, you'll have two choices to choose from.

You can choose to tell the truth about her father, aka Francois Sanon, who played a huge role in the Terramorph outbreak. Or you can keep this truth to yourself until you complete the UC Vanguard missions. While neither choice will affect the main missions, they will change your playthrough.

Disclaimer: The following guide contains heavy spoilers about the main story and plot. If you mind spoilers like this, now is the time to go back and watch again later.

There are no lasting consequences for telling Hadrian Sanon about her father in Starfield during the UC Vanguard questline. It will not affect the rewards you receive for completing the UC questline. However, telling Hadrian the truth will lock you out of a quest where you have to help Vae Victus track down war criminals from his cell. You will have plenty of chances to tell Hadrian about her father as you progress through the questline. However, if you put it off, she will eventually learn of her father's involvement in the Terramorph outbreak.