Henry did not petition for a divorce, he requested an annulment. The use of the term 'divorce' is common in the historiography, but it is a misnomer. What Henry was trying to do was declare the marriage between himself and Catherine had never been legitimate. Popes had granted annulments before, and in reality one of the main reason Pope Clement VII did not grant the annulment was because he was being held prisoner (in all but name) by Catherine's nephew, Emperor Charles V. I wrote up a longer piece on all of Henry's marriages here, and I would be happy to elaborate if you need.