Complex sentence: During the weeks leading up to the murder, Darnley had been healing after a bout of smallpox or speculated syphilis, as he was described having deformed pocks upon his face and body.
Split into simpler sentences: During the weeks leading up to his death, Darnley was recovering from a bout of smallpox (or, it has been speculated, syphilis). He was described having deformed pocks upon his face and body.