Princess Louise of Belgium (18 February 1858, Brussels – 1 March 1924, Wiesbaden) was the eldest daughter of Leopold II and his wife, Marie Henriette of Austria.

Born Louise Marie Amélie of Belgium, Louise married Philipp, Prince of Saxe-Coburg and Gotha, her second cousin, in Brussels, on 4 February/4 May 1875 and had two children:

The marriage was disliked by her father, who regarded it as an unwelcome alliance with Prussia, but her mother approved of it because Philip lived in Hungary. The relationship between Louise and Philip was not happy: Philip is said to have been authoritarian, and Louise responded to his authoritarianism by living a lavish lifestyle at the court of Vienna, where she attracted much attention. In 1880, she suggested the marriage between her sister Stephanie and Crown Prince Rudolf of Austria.

In 1895, Louise became romantically involved with Count Geza Mattachich (1868–1923), stepson of Oskar Keglevich, Count of Buzin. Mattachich was a lieutenant in a Croatian regiment of the Austrian army. They met in the Prater in Vienna.

In January 1897, she scandalized Vienna by permanently leaving her husband, Prince Philipp, for Mattachich and taking her daughter with her. They traveled first to Paris, then Cannes, living in other destinations in the south of France and the rest of Europe. Her son became estranged from her, because he felt her actions had ruined his chance for inheritance. Her daughter soon left her mother at the advice of her fiancé, the duke of Schleswig-Holstein.

In 1898, Prince Philipp and Mattachich fought a duel in Vienna, first with guns, then with swords, in which the prince was injured.

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