Prince William suffered from coronavirus quietly. The 38-year-old royal contracted COVID in April, shortly after his father Prince Charles did. A source tells ET that William had “fairly significant symptoms,” but opted to keep the diagnosis private in order to not worry the nation.

The prince was also reportedly heard telling someone during a royal engagement, “There were important things going on and I didn’t want to worry anyone.” He self-isolated at home, and his wife Kate Middleton and their three children did not get sick.

“William was hit pretty hard by the virus,” a source told The Sun. “At one stage he was struggling to breathe, so obviously everyone around him was pretty panicked.”

Charles was diagnosed in late March, and recovered after a few weeks. Prime Minister Boris Johnson was also ill with COVID around the same time, and had to be treated in an intensive care unit, leaving his Foreign Secretary in charge of the U.K. Several other members of the government also tested positive.

Twitter reacted with a mix of criticism and applause for the decision to keep the diagnosis private. Wrote one critic: “So Prince William had Covid19, at the tail end of Prince Charles also having Covid19, opening up the possibility of a gap in the line of succession from a 94-year-old to a 7-year-old and he didn't think it was worth worrying anyone about it.”

Royal historian Kate Williams tells CNN: “If the unthinkable had happened and the Queen, Charles and William all passed away, the next in line would be Prince George, who is seven years old. He would not rule as King in the traditional sense until he was 18, but a 'Regency Council' would be appointed who would carry out duties in his name.”

Other senior adult Royals in the line of succession are Prince Harry, who stepped down from his senior royal role earlier this year, and Prince Andrew, who has accused of having sex with at least one underage girl through convicted child trafficker Jeffrey Epstein.