The birth of the Monegasque twins raised an interesting succession question. Princess Gabriella was born before her brother Prince Jacques, but due to male-preference cognatic primogeniture, Prince Jacques is the Hereditary Prince of Monaco. Despite the fact that I find this a horribly outdated practice, Monaco is not the only country that still practises some form of this. Spain also has male-preference cognatic primogeniture, and Liechtenstein limits it succession to males only. Japan limits it succession to males only as well, and I’m afraid there won’t be many members of the Japanese royal house left soon. As far as I’m aware none of these currently have plans to alter these laws or have at least put these plans on hold.
An interesting situation took place in Spain back in 1885 that highlights the problems with this system. Alfonso XII of Spain died on 25 November 1885 leaving two legitimate daughters and two illegitimate sons. According to male-preference cognatic primogeniture, his eldest daughter Maria de las Mercedes should have inherited the throne. However, at the time of his death his wife, Maria Christina of Austria was pregnant. If this child were a boy, he would become king upon birth. If it were a girl, Maria de las Mercedes would become queen. Thus, from 25 November 1885 to the birth of this child, Maria de las Mercedes was the latent Queen, and her mother was regent to the vacant throne.
Alfonso XIII was born on 17 May 1886 becoming king from the moment of his birth and ending Maria de las Mercedes’ latent queenship.
Maria de las Mercedes would be Princess of Asturias as her brother’s heiress for the rest of her life as she died before her brother produced offspring.
She was married on 14 February 1901 to Prince Carlos of Bourbon-Two Sicilies. She died after giving birth to her third child. While she was pregnant, she had been diagnosed with appendicitis. She gave birth prematurely, and it was at first thought that the child had been stillborn before her brother King Alfonso realised that the baby had lived. She is buried at El Escorial.