It is what former royal butler Paul Burrell hasn't said that hangs over Prince Charles' shoulder like a black cloud as the heir to the British throne starts his nine-day official tour of India.
Also see: Slide show -- Royal Duty | Prince Charles in India
Burrell, who served the British royal family for 21 years and then turned on them by publishing some of their secrets in his book, A Royal Duty, is said to possess extra information that is so damaging that it could bring down the House of Windsor.
But, if true, this so-called dynamite about the sex lives of the royals has already been relayed to the US media, to the Germans, the Italians and rediff.com and is simply another tawdry page in the already scandal-prone lives of the British royals.
Most of the UK public has been educated in the details of Princess Anne's divorce, of how Prince Andrew's ex-wife allowed her toes to be sucked by her bald American financial adviser and the quarrels of the late Princess Margaret and her husband, the Earl of Snowdon. The list goes on and on.
So what remaining scandal is so damaging that it is spoken about in hushed tones among those who claim to know? The answer is that its importance has been vastly exaggerated.
The private lives of the British royal family in the 21st century are like the private lives of modern Pop stars or football legends. Everyone likes to read about them, but no new revelation is likely to undermine the foundations of a dynasty that does such a superb job in keeping the public amused, intrigued and constantly entertained by their antics.
Individual members of the royal family may be upset by what Burrell has chosen to divulge about their daily lives, but the real damage has been done by Burrell to himself.
His book is not turning into a sales stampede -- in fact it is selling at a discount -- because for all the scandalous details about Diana's suitors and Charles' foot stamping tantrums, nobody likes a gold digger making money out of a dead woman's past.
Burrell took enormous pride in being described as Diana's 'rock', valet, confidante and counsellor. He may even have been in love with her. But his justification in telling some of her innermost secrets, even at the cost of the hurt it would cause to her two sons, is questionable.
At one point he said he had to tell the story for the sake of history; in other recent interviews he explained he would have foregone the pleasure of earning £300,000 from writing his book if Charles or his two boys had telephoned him after he was falsely arrested for stealing some of Diana's personal possessions.
As the book sales prove, not many believe his line.
More revelations, more sex scandals will undoubtedly provide the extra gossip on which all societies survive. Hence the worry for Charles and the rest of his entourage visiting India about what more Burrell can tell. In truth, it is the butler's loyalty, integrity and judgement that is at stake. No one else needs to worry.