She was born Mathilde d'Udekem d'Acoz. Even though her grandfather and her uncle were barons, she and her father were members of the untitled nobility. As such, she has a right to the Dutch predicate Jonkvrouw.
The announcement of her engagement with the Belgian heir apparent, who had never been seriously linked with any woman, came as a big surprise. At the time of her wedding, she was given the title Princess of Belgium ad personam. The wife of a Belgian prince used to get this title automatically, but now there needs to be a special creation. Her family was elevated to the rank of Count. When her husband will become king, she will be the first Belgian-born Queen Consort.
She used to be a speech therapist and has studied psychology. She has one daughter, Princess Elisabeth, and one son, Prince Gabriel.
In 1997, one of her sisters and her grandmother, died in a car crash. She has two other sisters and one brother.