The 66-year-old wrote in a tweet Tuesday that he is experiencing mild symptoms and is "following the experts' advice" by isolating himself until he's healthy.
A spokesperson for Gates maintained that his decades-old "affair," which was the subject of an investigation, had no connection to his decision to step down from the board.
"After a great deal of thought and a lot of work on our relationship, we have made the decision to end our marriage," the couple wrote in a joint statement.
The Amazon CEO and four other billionaires are part of the world's most exclusive club in the midst of the pandemic: those whose fortunes exceed $100 billion.
"My dad's wisdom, generosity, empathy, and humility had a huge influence on people around the world," Gates wrote in a tribute to his father.