Complex sentence: The would-be "khatib", wearing full male dress with a false beard and moustache, sat on the "minbar" just before speaking, at which point some worshippers realised that the new imam was a woman in disguise.
Split into simpler sentences: The would-be "khatib" was wearing full male dress with an artificial beard and moustache. When sat on the minbar just before she was to deliver the khutbah, some worshippers realised that the new imam was a woman in disguise.