The brother fought, but Rama could not tell who was who; he didn't shoot.
Sugriva fled in fear, and Vali scoffed.
"You didn't shoot him!" Sugriva said to Rama.
"I couldn't tell you apart," Rama explained.
Sugriva put on a flower-garland and challenged Vali again.
Rama aimed at Vali, shooting an arrow in his back.
Vali fell, fatally wounded.
Vali's wife bewailed her dying husband. "May you never find peace even after you regain your wife," she said.
With that curse, she avenged Vali's death.
Inspired by: Sita: An Illustrated Retelling of the Ramayana by Devdutt Pattanaik
Notes: This story is on p. 175 of the book. In Valmiki's Ramayana, this is the Kishkindha Kanda (Book 4), sarga 12. The duel and its aftermath occupies several chapters in Valmiki, with long discourses by Rama, by Vali, and by Vali's wife Tara.