On 16 March 1792, Gustav III was shot at the Royal Opera House in Stockholm, and died almost two weeks later. In Sweden, Gustav's younger brother, the Duke Karl, became regent to the underage Gustav IV. On 20 April, France officially declared war on Austria, and invaded the Austrian Netherlands. On 20 June, the Tuileries was stormed by a large crowd and Louis was made to wear a red bonnet of liberty and drink a toast to the health of the people of Paris and the Nation. Three days later Marie-Antoinette was able to get an encrypted letter out to von Fersen: "Your friend is in the greatest danger. His illness is making terrible progress ... Tell his relations about his unfortunate situation".