Speaking to the BBC's Amol Rajan in an interview that aired on Wednesday amid an ongoing phone-hacking case brought against Daily Mirror publisher Mirror Group Newspapers by Prince Harry and others, the former editor said Diana was in regular contact with the press.
He also claims Diana manipulated the papers to "get one over on Camilla".
"I don't criticise what Diana was doing... but she would court people like me, she would talk regularly to people like me, she would blatantly stiff me... she would deliberately manipulate the papers so that she could get one over Camilla – and I wonder when I hear Harry, for example, talking in the way he does about media intrusion into his mother's life, his life, whether he knew the half of it – I doubt he did. He was only 12 when she died, I doubt he knew that she was doing all this," Morgan said.
Asked why Diana maintained a relationship with Morgan despite tackling huge press intrusion into her life, the broadcaster said she wanted to influence the narrative.
"I think that, like everyone in public life, it doesn't matter whether you're a royal, your a politician, you're a tennis player, you're a singer – whatever it is, you want to have the best media press coverage you can get and Diana was a good example of somebody who did influence me, actually very effectively," Morgan said.
He described agreeing not to run certain pictures from an "unlicensed group of paparazzi running around making her life hell", and said he had also promised to call the princess if there was a particularly sensitive story coming out about her in the Mirror, which Morgan edited from 1995 to 2004.
One such story involved Diana's private visit to an eating disorders clinic, which Morgan got wind of and called her about.
"I did all the right things, and she was incredibly grateful," he said of the story, which Morgan claims was a result of Diana giving him an hour-long interview that subsequently ran on the front page.
"I got to bed, I have a glass of wine, I'm celebrating, the scoop bomb goes off – everyone's chasing it, it's first seven pages of the Mirror – Diana and bulimia, the truth in her own words, blah blah blah.
"And I know it's 100% accurate because she's the one who told me, she's my source, and then about 9 o'clock in the morning comes a Press Association snap: Diana, Princess of wales, is deeply upset over intrusive revelations in today's Daily Mirror about a private visit to an eating disorder clinic."
Morgan said he called the palace and threatened to release tapes of the interview that revealed Diana as his source, but opted not to after he was told Diana had slept on it and felt she wanted her visit to the clinic to be private.
"You got lobbied – she silenced you," Rajan told Morgan, also calling him a "coward" for not following through with his threat.
"I had access to the biggest star on the planet, she had stiffed me on this no question, but she didn't deny the thing that we did, she just said she was upset by the intrusion into the private visit so we took a whack as a paper for intrusion, but we still got the scoop and we still sold buckets of papers – and I kept the relationship, which carried on until she died," he added.
Yahoo News has contacted Buckingham Palace for comment.