The iPhone 5S isn't the only thing Apple launched on Friday.
CEO Tim Cook made his Twitter debut, sharing his pride in the company's launch of its newest handset.
"Visited Retail Stores in Palo Alto today. Seeing so many happy customers reminds us of why we do what we do," he said.
The circumspect Cook's tweet caught the Internet by surprise.
Read the Storify below for more reactions to Cook's social media debut.