When the Duke of Sussex returned to Britain for four days of public engagements last September, he seemed to be on a public relations offensive after a string of negative stories about him and his wife.

He made a point of visiting Nottingham, where he had brought Meghan Markle in December 2017, just days after they had announced their engagement.

Prince Harry visited Community Recording Studio in the St Ann's area of Nottingham to meet social action groups and local charities.

The trip captured headlines when it was announced that Prince Harry had made what was described as a 'personal donation' of a staggering £1.1million to the BBC's Children in Need charity. The money would, it was said, be used to support projects that tackle violence affecting young people.

Sources told the BBC that the donation was 'from his own money rather than his Archewell organisation'. It would, Harry said, help 'changemakers in the city continue their mission to create safe spaces... and offer hope and belonging to young people who need it most'.

The size of the donation did, however, cause some surprise on both sides of the Atlantic.

After all, it had been widely reported two months earlier that Netflix would not renew its $100million (£75million), five-year deal with the Duke and Duchess of Sussex (they later signed a much less lucrative 'first-look' deal with the US streaming giant).

And the California-based couple had lost their $20million (£15.6million) deal with audio giant Spotify amid much acrimony two years previously.

How on earth, some people wondered, could the Sussexes afford to hand over £1.1million of taxed income to just one cause, however worthy?

I have now discovered the answer.

The money didn't come from Harry's own pocket, but from another charity.

It did not come from money that Harry had made from the couple's corporate deals or royalties from his tawdry memoirs, Spare.

All £1.1million came from charitable funds originally from his mother, Princess Diana.

The donation was made not by Harry but by the Glen Beg Foundation. This is a charity that was established in 1999, two years after Diana's death.

It was set up using funds from the Princess of Wales Charities Trust. This was established by Diana in 1981, the year she and Prince Charles were married at St Paul's Cathedral. It was financed by generous donations from companies and organisations that she visited or represented. When she died, the money in the trust was split equally between Harry and his brother, Prince William.

The boys' charities were named after hills on the monarch's private Balmoral estate in Scotland. William's was called The Broad Cairn Foundation; Harry's the Glen Beg Foundation.

Documents filed at the Charity Commission confirm that £1.1million was transferred from the Glen Beg Foundation to Children in Need on October 10 last year, a month after Harry announced the donation.

It's not clear how much, if any, money remains in the Glen Beg Foundation. When it was established, the trustees were Hugh van Cutsem, a long-term friend of Charles who died in 2013, and Harry's late godfather, old Etonian farmer Gerald Ward. Charles's solicitor Baroness (Fiona) Shackleton of Belgravia was the only trustee to sit on the boards of both Harry and William's charities.

A spokesman for the Duke and Duchess of Sussex failed to respond to a request for comment.