Història de Portugal Vol. III A.H. de Oliveira Marques (Listing Maria Pia as the daughter King of Carlos I)
Fernando Luso Soares: MARIA PIA Duquesa de Braganca contra D. Duarte PIO, o senhor de santar, 1938
Mario Soares: PORTUGAL AMORDAÇADO deportimento sobre os anos do fascismo; Arcadia
Letters to Dona Maria Pia written by gen. Francisco Franco
Letters of Support to Dona Maria Pia written by HM the King Alfonso XIII and the Prince Alfonso Jaime de Borbon