In a front-page splash on the day Britain opened an inquest into Diana's death, The Mirror named the person she had claimed was "planning an accident" in a chilling prediction of her own death in a car crash in August 1997.
She made the allegation in a letter she gave to her butler and confidant, Paul Burrell, before she died.
The former wife of heir-to-the-throne Prince Charles died at the age of 36, along with her lover Dodi al-Fayed and their chauffeur Henri Paul in a Paris road tunnel.
The Mirror appeared to be risking an aggressive legal response from Buckingham Palace to its story on Tuesday.
The rest of the normally competitive British media omitted the name, apparently to avoid legal action under Britain's tough defamation laws.
The tabloid printed a copy of the letter Diana wrote just 10 months before her death on its inside pages. Although it identified the person in its own story, the name was blanked out in the reproduction of the handwritten letter.
"This particular phase in my life is the most dangerous," it quoted the letter as saying. "(...) is planning 'an accident' in my car, brake failure and serious head injury."
"This particular phase in my life is the most dangerous... (...) is planning 'an accident' in my car, brake failure and serious head injury"
Excerpt from Princess Diana's letter to her butler
Burrell, who gave The Mirror access to the letter as part of a serialisation of excerpts of his book which was published late last year, reacted angrily to news the name had been revealed.
"I am not very happy about it... I only learnt about it late last night. And it was always my intention never to publish that name," he told reporters on Tuesday.
Britain's tabloid newspapers have been engaged in an almost daily battle in the years since Diana's death to produce the most sensational headlines about Diana, Charles and other members of her family and former household.
Tuesday's revelation came as Royal Coroner Michael Burgess was due to open and adjourn inquests into the deaths of Diana and Dodi.
Hundreds of journalists from around the world gathered for the start of the inquests in central London - the first official public hearings into the crash to be held on British soil.
An inquiry by French authorities in 1999 ruled the accident was caused by Diana's chauffeur being drunk and driving too fast.
The Mirror said Burrell was prepared to hand over the Diana letter to the coroner as part of the inquest.
It said that in doing so, he would be "honouring a long-standing promise to cooperate fully with the inquiries".
After a 15-year marriage, Charles and Diana divorced in 1996 after both had admitted to having adulterous affairs.