Astrid Stawiarz/Getty Images for RFK Human Rights
Calling the shooting an act of terrorism, Cook offered his deepest sympathies and asked for a moment of silence.
"We celebrate our diversity. We know that it makes us stronger and moves everyone forward," Cook said.
During the moment of silence, Cook had to wipe a tear from his eye.
Cook, one of the few openly gay CEOs, first spoke out about the attack on Sunday morning on Twitter.
Our hearts go out to the victims of the unspeakable tragedy in #Orlando, their families and all who grieve with them.
- Tim Cook (@tim_cook) June 12, 2016The attack on the Pulse nightclub in Orlando killed 50 and left more than 50 injured.