Does uttering the phrase "you are divorced" constitute a divorce if it was said in jest or if the full sentence was not heard?

The Fatwa's Summary:

If the sister is certain that she heard the clear divorce utterance from the husband, with its conditions, including the intention of the word of divorce and its meaning, then the divorce has occurred, even if the husband was jesting and not serious. She must prevent him from herself and observe the 'iddah (waiting period), and he may take her back during the 'iddah.

However, in case of doubt and uncertainty about the matter, the certainty of the marriage is not removed by doubt.