Complex sentence: Immediately after John XXIII's election as pope in 1958, it was not known if he would be John XXIII or XXIV; he decided that he would be known as John XXIII.
Split into simpler sentences: Immediately after John XXIII's election as pope in 1958, there was some confusion as to whether he would be known as John XXIII or John XXIV. He himself ended the confusion by deciding that he would be known as John XXIII.