From a month-long journey the king brought the famous German Dr. Friedrich Struensee as personal physician. He also treated Caroline Mathilde, who had suffered a serious, life-threatening collapse. Struensee, an educated, progressive young man, familiar with the ideas of Voltaire and Rousseau, made an impact particularly through the force of his personality. Caroline Mathilde not only recovered quickly – she also became more self-confident and was able to strengthen her position vis-à-vis the king. Struensee was knighted and appointed State Councilor. Whether he was the father of his daughter Luise Augusta, born in 1771, is controversial. He began far-reaching reforms in many areas (e.g. he introduced freedom of the press and equality for illegitimate children and abolished serfdom and torture) – too much at once, too quickly and too radically. Nobility and clergy, whose privileges were curtailed, envious people and schemers looked for ways to overthrow him. In January 1772 the conspirators struck. They took King Christian into their power; Caroline Mathilde and Struensee went to prison. Struensee was horribly executed for treason, Caroline Mathilde was divorced and was to be banished to Aalborg Fortress for life.

Finally George III took action. from England. By threatening that his fleet would bombard Copenhagen, he secured his sister’s release. However, he did not let her return to England, but instead gave her the castle in Celle as her place of residence. The children, heir to the throne Frederik and Luise Augusta, remained in Denmark. Caroline Mathilde died completely unexpectedly shortly before her 24th birthday.