Divination Portent: with adv/disadvantage, does Portent replace the final result, or one die?

Sudden thought on Divination Portent. With adv/disadvantage, does Portent replace the final result, or one die?You replace the entire roll with the chosen result.

— Dan Dillon 👥 (@Dan_Dillon_1) January 25, 2020

Because keep in mind, you use Portent before the roll. The roll never happens.

— Dan Dillon 👥 (@Dan_Dillon_1) January 27, 2020