Charles XII was extremely fond of his two sisters Hedvig Sofia and Ulrika Eleonora. It is well known that the news of Hedvig Sofia's death, which had arrived just before Poltava, was kept from him for quite some time because his entourage feared that such a blow could cause grave damage to his health. Charles XII and his eldest sister were very close, which her letters to him clearly show. Upon hearing the news from Narva she wrote to him on 7 December 1700. The first report had reached Stockholm on the 4th and futher confirmation had arrived the next day. The joy was indescribable, the Duchess wrote. God would undoubtedly continue to help and bring the Polish business to a quick resolution.
On the 28th the Duchess wrote again, thanking the King for a greeting sent by Arvid Horn and for the account of the battle by Carl Gustaf Wrangel. It was obvious, she wrote, that a very thorough fact checker had been at work. This was particularly pleasing as it proved that the King had not forgotten his devoted sister. May the Lord continue to protect His Majesty and help him carry out all his plans. I only wish, the Duchess wrote, that I will one day have an opportunity to meet Your Majesty again.
In her next letter, dated 29 January 1701, Hedvig Sofia jokingly informed Charles that some of the women at court had become soldiers and had enrolled her. They had their own uniforms and was now preparing to sail to Livonia. They would surely frighten the Russians more than the Russians would frighten them. The life at court was merry, but the King was missed. When he returned it would surely become even merrier.
On 4 February Hedvig Sofia gently reprimanded her brother. She was pleased with the greetings sent through Arvid Horn, but wished the King would write himself. She did not particularly like the stories about his disregard for his health. On him rested all hopes and he should take better care of himself.
Source: Riksarkivet, Skrivelser till Konungen. Karl XII, vol. 38