Beatrice was one of the eleven children of Rui Gomes da Silva, the first governor of Campo Maior, Portugal, after its reconquest from Arab rule, and of Isabel de Menezes, the Countess of Portalegre, an illegitimate daughter of Dom Pedro de Menezes, 1st Count of Vila Real and 2nd Count of Viana do Alentejo, in whose army her father was serving at the time of her birth. One of her brothers was the Blessed Amadeus of Portugal, O.F.M., a noted reformer of the Order of Friars Minor. She was long thought to have been born in the Portuguese colony of Ceuta in North Africa, where her father was serving as a military adjutant at that time. Modern research has determined that she was, in fact, born in the family home at Campo Maior.