Eleven days after Orsini's assassination attempt in France, Victoria's eldest daughter married Prince Frederick William of Prussia in London. They had been betrothed since September 1855, when Princess Victoria was 14 years old; the marriage was delayed by the Queen and Prince Albert until the bride was 17. The Queen and Albert hoped that their daughter and son-in-law would be a liberalising influence in the enlarging Prussian state. Victoria felt "sick at heart" to see her daughter leave England for Germany; "It really makes me shudder", she wrote to Princess Victoria in one of her frequent letters, "when I look round to all your sweet, happy, unconscious sisters, and think I must give them up too – one by one." Almost exactly a year later, Princess Victoria gave birth to the Queen's first grandchild, Wilhelm, who would become the last German Kaiser.