 Catherine responded by declaring she had a lunatic for a son.<ref>Durant, p. 355.</ref>

Charles' physical condition, tending towards tuberculosis, deteriorated to the point where, by spring of 1574, his hoarse coughing turned bloody and his hemorrhages grew more violent.Charles IX died at the Château de Vincennes, 30 May 1574, aged 23.As his younger brother, Henry, Duke of Anjou, had recently been elected King of Poland and was away from France, their mother Catherine resumed the regency until Henry's return from Poland.