Yesterday, Johann Hari sent a dramatic message on Twitter:

Kate Middleton is being advised by a far right-winger who blames concentration camp victims for their own deaths.

This linked to the following on Hari's own blog, which stated:

It has been revealed that a far right-winger who blames concentration camps victims for their own deaths is giving history lessons to Britain's future queen, Kate Middleton. Rod Liddle discloses in passing here that Andrew Roberts is "tutoring" her in the run-up to the royal wedding. To find out just who this "historian" is, read my exposé of him here. If Kate plays close attention to her new teacher's lessons, we can expect the wedding to be livened up by declarations that massacring unarmed civilians is "necessary" . . .

The semi-humorous Rod Liddle piece to which Hari linked in support of this news stated:

The historian Andrew Roberts is to give Kate a lesson in the history of the House of Windsor. "Mainly German and not terribly bright" should do it, I would have thought.

It appears that Liddle's intended meaning was that the first sentence was correct and the second sentence was a mirthful exaggeration or gloss.

However, it currently appears the only source for the Liddle assertion was in turn a parody piece by "Talbot Church" in the Independent of a couple of weeks earlier:

Mindful that not everyone knows the proud history of the royal family, aides have asked pint-sized historian Andrew Roberts to talk the bride-to-be through the history of the House of Windsor.

There appears to be no other published source.

So, is Andrew Roberts to be providing tuition to Kate Middleton?

I asked Clarence House, which categorically denied that Roberts had been asked or would be asked.

A royal aide told me:

Andrew Roberts has not been invited to give constitutional history or other lessons to Miss Middleton. There are no plans to approach Andrew Roberts.

Clarence House also asked me to state:

Prince William's private office will organise a series of private meetings with key individuals for Miss Middleton to meet both before and after the marriage, with regard [to] preparing her to become a member of the royal family. These will include senior members of the royal household, key advisers to Prince William and Prince Harry, and representatives from some of Prince William's charities and other affiliations.

I also asked Andrew Roberts, via his agent, but have so far had no reply.

So, what is correct?

Will the historian Andrew Roberts be giving tuition to Kate Middleton, as Hari and Liddle confidently assert?

Or was Hari's worrying tweet based only on a semi-parody, which was in turn derived from a parody in Hari's very own newspaper?

Could Johann Hari and Rod Liddle really have got something like this wrong?

Who knows?

But I offer a royal wedding commemorative mug to the first person who can evidence the news that Andrew Roberts is to give such tuition.

UPDATE: Andrew Roberts has now also categorically denied the appointment.

FURTHER UPDATE: Johann Hari now admits that his tweet and blog post were based on a factual error and that Andrew Roberts was never invited to tutor Kate Middleton.

David Allen Green is legal correspondent of the New Statesman.