Imagcq, thank you for the link - as a good Catholic girl (well sometimes) I am aware of the divisions and schisms in the Church and Papacy to a point. I feel however that I am still missing something here.
If we take 'Personal relationship' to be 'Chemistry' then we are left with 'Petro' to complete the word play - ' between two successive popes'.
I realise I may be in danger of making heavy weather of this, sorry and thanks for all help.