The Pope - Does he tactically ex-communicate?

[Omanes Alexandrapolites]

Hi guys,
A while ago, in a French campaign, as in most of my campaigns it ended in a civil war and utter-defeat with a treasury in minus figures, in XL, I noticed something rather strange. I had attacked the pathetically poor Geonese as a tactical way of forcing the influential pope to warn me so that I would be free to remove the English in peace. The Pope, rather than warning me for my aggressive nature, cancelled his alliance with the Geonese. Two turns later they were ex-communicated and the following turn the Pope declared war on them, invaded their lands, wiped them out and the following turn started tearing chunks out of the, excommunicated for their attacks on me, the Holy Roman Empire. I had never seen anything so strange in any campaign before, although you can excuse me for this, I have sadly being playing for just over a month, so I was amazed when I saw these events occur. Has anybody else had a ferocious pope who ex-communicates and then uses it to attack and do any experts understand what may have caused this peculiar action by the "Holy" Father. All help/advise appreciated, thanks!