On Wednesday, Biles announced she would not defend her gold medal, instead opting to focus on her mental health.
The 24-year-old had withdrawn from the team final the previous night amid dramatic scenes, as she bowed out after performing on only one piece of apparatus and subsequently revealed her struggles, admitting she felt the “weight of the world” of her shoulders.
Lee had been one of the three Americans left to continue the competition without their most high-profile star and along with Jordan Chiles and Grace McCallum battled on to silver, behind the Russia Olympic Committee.
Returning to the Ariake Gymnastics Centre for the first time since, and with Biles cheering on in the stands, Lee put in a magnificent display to take the title with a total score of 57.433, including a sensational 15.300 on uneven bars, the joint-highest score on any piece of apparatus all night.
Brazil’s Rebeca Andrade finished second, only 0.135 behind after two pivotal errors in her final performance on floor, with Angelina Melnikova of the Russian Olympic Committee in third.
Team GB’s Jessica Gadirova finished tenth in her first Olympic final, with twin sister Jennifer Gadirova in 13th and the pair of 16-year-olds added excellent individual performances to the team bronze they had won with Amelie Morgan and Alice Kinsella.