The accepted reason for this is that the Pope and his son Cesare had contrived a plot to murder Giovanni, but Lucrezia was informed by Cesare and warned her husband to leave.
ðɪ ɐksˈɛptᵻd ɹˈiːzən fɔːɹ ðɪs ɪz ðætðə pˈoʊp ænd hɪz sˈʌn sˈɛsɛɹ hæd kəntɹˈaɪvd ɐ plˈɑːt tə mˈɜːdɚ dʒəvˈɑːni, bˌʌt luːkɹˈiːziə wʌz ɪnfˈɔːɹmd baɪ sˈɛsɛɹ ænd wˈɔːɹnd hɜː hˈʌsbənd tə lˈiːv.