"I'm a diabetic, and I went from my usual bloods that I usually have between months," the Succession star told James Corden on The Late Show. "I went there, and they took my bloods, and they took the COVID test. Then my doctor called me and said, 'Oh, congratulations. You've had it.'" But Cox thinks he might have unknowingly contracted COVID-19 back in December because he experienced "sneezing attacks."