The Lord Lucan scandal is the greatest and most enduring murder mystery of the 20th Century - and this latest twist in the tale offers up ever more fascinating possibilities.
Above all, it raises the slight chance that the missing Earl of Lucan may have been telling the truth. There is a possibility, albeit a small possibility, that he was innocent.
I have long been interested in the saga of the missing Seventh Earl of Lucan; I've even written the book.
And for journalists like me, this mystery has always been seen as the Moby Dick of World Exclusives. We know this great white whale of an exclusive is out there - and, one day, somebody will make their name on Fleet Street by landing the big one.
I should perhaps start by acknowledging that at the heart of the Lord Lucan mystery is a tragedy - not just for the family of Sandra Rivett, the murdered nanny, but also for Lord Lucan's family and friends. The scandal cast a very deep shadow over the lives of his three children which continues to affect them even to this day.
But what has kept this mystery in the public eye, as we constantly rake over the details, is not so much the murder as what happened afterwards. The evidence that we have is so sparse, so scant, that pretty much any scenario is as feasible as the next one.
All we know is that 38 years ago, the Lucans' nanny was bludgeoned to death in the basement of Lady Lucan's flat. Immediately afterwards, the Earl disappeared and has never been seen or heard of since. It has long been assumed that he was up to his neck in the murder.
After the murder, Lord Lucan did leave a very small trail. He sent a few letters while he was on the run, and his blood-spattered getaway car was found dumped in the port of Newhaven, Sussex.
And as for the rest - we can argue and surmise what we like. But for every sighting that there has been of Lord Lucan in Africa and India, and even in Scotland, there is always another counter-claim from one of his old friends to say that, actually, Lucan did the decent thing and committed suicide soon after the murder.
Who knows. It's a mystery - and, so long as it remains a complete mystery, then it will continue to be discussed over dinner-tables across the land.
This latest piece of information to be uncovered by BBC's Inside Out is remarkable, however, because for the first time, it appears to provide some slight corroborative that Ms Rivett may indeed have been murdered by another man.
While he was on the run, Lucan repeatedly claimed that he'd just happened to be passing by the house in Belgravia when he looked down into the basement and saw Ms Rivett struggling with an intruder.
There has never been any evidence to either prove or disprove this claim.
But if this new nugget from the BBC is true, then it would indicate that there may well have been some other man involved. For the past 38 years, there's always been a difficulty in pinning a motive onto the murder. Why would anyone want to kill Sandra Rivett?
It's always been assumed that Lucan killed Ms Rivett after mistaking her for his estranged wife.
But if Ms Rivett had a lover and if she was sharing that lover with somebody else, then it puts quite a different complexion on the whole murder. Suddenly, we now have not only a motive but also a mystery man in the house.
For the first time, these old police files provide a small tantalising kernel of evidence which shows that Lucan may not have been the killer. He may have been, as he said all along "lying doggo" because he thought he'd never get a fair trial.
It is possible. And yet as one piece of new evidence comes to light, it merely raises more questions. How is it that this extraordinary piece of information has been kept under wraps for nearly four decades?
I hesitate to use the phrase, but it almost smacks of an establishment cover-up. Perhaps it was felt better for all concerned if Lucan just happened to disappear off the face of the earth.
* William Coles' book, Lord Lucan: My Story, was published by Legend Press in 2009.Suggest a correction