Complex sentence: In 2011, Casiraghi and his siblings Charlotte and Pierre hosted Monaco's annual Rose Ball, in the absence of Prince Albert, Princess Caroline and Princess Stéphanie who were mourning the sudden death of their aunt Princess Antoinette, Baroness of Massy a few days earlier.
Split into simpler sentences: In 2011, Casiraghi and his siblings Charlotte and Pierre hosted Monaco's annual Rose Ball, in the absence of Prince Albert, Princess Caroline and Princess Stéphanie. Their decision not to attend the gala followed the sudden death of their aunt Princess Antoinette, Baroness of Massy, few days earlier.