According to Miami's CBS affiliate, NASA Administrator Charles Bolden told Scott Kelly on Monday that he "almost had a heart attack" when his identical twin, Mark, showed up on the morning of the Soyuz launch without his usual mustache.

"He fooled all of us," Bolden said, according to CBS Miami. The facial hair was "the only way I can tell you two apart."

Scott will work and live on the International Space Station for a year while his twin Mark stays on Earth as part of an experiment to see how space affects Scott's body.