Constantly together since they were children, they had grown up very much alike. Lucrezia’s intelligence impressed close observers like Il Prete, but, dazzled by her golden hair and her famous charm, they failed to divine the Borgia toughness beneath the feminine skin. She shared with her brother the nerves of steel and incapacity for real feeling which had enabled her to survive the experiences of the last few years unscathed. Their mutual affection was based on similarity of character and outlook, and strengthened by the sense that the rest of their world regarded them as dangerous outsiders.
Cesare Borgia: His Life and Times (Sarah Bradford)
but no my favorite lucrezia anecdote is the one from isabella d’este’s spy before lucrezia marries alfonso d’este isabella sends her man in to take lucrezia’s measure. they have tea. he writes home: 'i told her everything. she told me nothing. you didn't fucking tell me she had the borgia brain.' (hotelsongs)