What is the complete irreverent limerick about the Borgia family that
ends with the line
"....her father, the Pope."

Greetings!  I couldn't find it online but did find a reference to the
book Limericks Historical and Hysterical - Plagiarized, Arranged,
Annotated, and Some Written by Ray Billington, 1981, 127 pages.  You
may find it there.

Good luck in your quest!

I've had no success finding this, but I did come across another
irreverent limerick which touches on the same theme:

http://www.toastpoint.com/limerick/1997/naut997.html

"Your most pious bishops are ones 
Who never just sit on their buns," 
Caesare Borgia once noted. 
"They all are devoted 
To taking good care of their sons." 

...by A. N. Wilkins