Sophie Maria Josephine Albina, Countess Chotek of Chotkow and Wognin, Princess of Hohenberg, is Alek's mother. Alek inherits his title from her. She married Archduke Franz Ferdinand in a morganatic marriage, which does not allow Alek to inherit any of his father's titles and hereditary lands. Before her marriage, Sophie was a countess. In the series, she and her husband are poisoned in Sarajevo as part of a German plot.
When Alek and his men escape in the Stormwalker, before Alek learns about her death, Alek is afraid that Sophie will be upset about the walker ruining her garden walking paths. He thinks about how angry Sophie was when this happened before.
Alek tells Deryn the story of his parents meeting when Sophie was a lady-in-waiting to the Princess Isabella of Croÿ. Franz Ferdinand kept (and accidentally lost) a locket with Sophie's picture in it, and, when Isabella found the locket she was upset to see one of her ladies-in-waiting instead of one of her marriagable daughters.
- Sophie, Duchess of Hohenberg on Wikipedia