Born on 13 August 1911, Isabelle Marie Amélie Louise Victoire Thérèse Jeanne of Orléans-Braganza was the eldest daughter of Dom Pedro de Alcântara, Prince of Grão-Pará, erstwhile heir to the throne of the Empire of Brazil, and his wife, Countess Elisabeth Dobrzensky of Dobrzenicz.

Isabelle was born in a pavilion on the grounds of the Château d'Eu, her paternal grandfather's home in the town of Eu in the Seine-Maritime department of France in Normandy.

In 1924, her father's cousin, Prince Adam Czartoryski, placed at the family's disposal, apartments in the palatial Hôtel Lambert on the Île Saint-Louis in Paris, where Isabelle and her siblings undertook their studies.

[3] The family travelled extensively and much of Isabelle's youth was spent visiting her maternal relatives at their large estate at Chotěboř, Czechoslovakia, Attersee, Austria, and Goluchow, Poland.

[3] In 1920, Brazil lifted the law of banishment against its former dynasty and invited them to bring home the remains of Pedro II, although Isabelle's grandfather, the Count of Eu, died at sea during the voyage.

The couple kept their engagement a secret until a family gathering at Attersee later that summer, but were obliged by the Duke of Guise to wait until Henri finished his studies at Louvain University before the betrothal was officially announced 28 December 1930.

[5] The wedding gave rise to several royalist demonstrations, and the road leading to the cathedral was lined with hundreds of visitors from France who viewed Henri as the rightful heir to the French throne.