"Barristan Selmy himself has been haunted by the “bloody bodies” of Aegon and Rhaenys. His serious injuries following the Battle of the Trident prevented him from personally examining the corpses, but he wondered for years about whether Robert smiled at the bodies. Selmy concludes that such a smile would lead him to kill Robert, and that no army could save him."
I doubt Robert smiled. It was after all Tywin’s idea.