H.R.H. Grand Duke Guillaume IV

In 1893, Prince Guillaume married the Catholic Princess Maria Ana of Braganza, Infanta of Portugal, whom he had first met in 1884. The six Princesses resulting from this marriage were all baptised Catholics. In 1904, he hired a Luxembourgish teacher, Ms Marie Knaff, to educate his six daughters. Ms Knaff would go on to form three generations of the Grand Ducal Family in the Luxembourgish language and culture.

After suffering a second serious stroke at the beginning of 1906, Guillaume IV was only able to spend a few months in the Grand Duchy. He visited in October of the same year; two shorter stays followed in 1907, before he required extended periods of rest abroad.

As the hopes of a male heir to the throne were not fulfilled, the male line of the entire House of Nassau was destined to die out. That is why Guillaume IV promulgated an internal law of the House of Nassau in 1907 to confirm his eldest daughter Princess Marie-Adélaïde as heir to the Throne, as well as a far-sighted family statute concerning the internal constitution of the ruling House. After a tense debate, the Luxembourgish Chamber of Deputies recognised the internal law by 41 votes to 7. This also ensured the succession against the pretender to the Throne, Count George of Merenberg, who was living in Wiesbaden. He was the son of the half-brother of Grand Duke Adolphe, Prince Nikolaus of Nassau who had contracted a morganatic marriage with Natalja Pushkina.

Because Guillaume IV was seriously ill, Grand Duchess Maria Ana was obliged to become Lieutenant-Représentant from March 1908, and Regent from November 1908 until Grand Duke Guillaume's death. Berg Castle, located 23 km north of Luxembourg City and which had served as their residence since 1893, was largely rebuilt between 1907 and 1911. In September 1911, Guillaume IV returned to the castle, terminally ill, and died there in 1912.

The death of Guillaume IV marks the definitive end of the 800-year reign of the male lineage of the entire House of Nassau. He found his final resting place in the princely crypt of Weilburg.

As Grand Duchess Marie-Adélaïde was a minor at the time of the death of her father Guillaume IV, Maria Ana, the Grand Duchess' mother, remained Regent until her daughter came of age on 14 June 1912.