Not just any biographer gets portrayed in a Netflix series. But Andrew Morton is no ordinary biographer. Morton released “Diana: Her True Story” in 1992. The source of his blockbuster biography was the princess herself, a fact Morton only revealed after Diana’s death. The details of those melancholy interviews, recorded secretly on cassette tape, appeared in the fifth season of “The Crown.” “In a funny kind of way, the actual buildup to the Diana book was more dramatic than they portrayed it,” Morton tells The Post. “We swept the room for bugs. There was a lot of counterintelligence work going...