It comes as the Met Police launched an investigation into allegations Mahfouz Marei Mubarak bin Mahfouz was offered help to secure UK citizenship and a knighthood by an aide to Prince Charles.
Clarence House has said Charles had “no knowledge” of the alleged honours and citizenship controversy.
Mahfouz has also denied any wrongdoing.
The Duke of Sussex, 37, said last year he had cut ties with Mahfouz as he tried to distance himself from the row.
Now leaked emails reveal that in 2014, Harry's HIV charity Sentebale was set to receive a £1million donation from the donor.
A representative of Mahfouz said he wanted a private meeting with Harry before transferring the funds, The Sunday Times reported.
Former royal equerry Mark Dyer, 54, told the rep in an email: “I am seeing PH today at Windsor; I will brief him on the situation and see if he now wants to commit to a trip, but this certainly was not our understanding… it is starting to bring into question ‘cash-for-access’."
The rep then reportedly claimed a Saudi trip had originally been suggested by Charles at a Clarence House meeting weeks before.
Harry allegedly joked when he met the Saudi at Clarence House: “Has father beaten me to it and got the money?”
But Mahfouz ended up donating £1.5million to Charles’s charities instead.
Charles awarded the billionaire with a CBE in 2016 and named a woodland at a Scottish castle in his honour.
Police were alerted when Michael Fawcett, 58, temporarily stepped down as chief executive after a letter showed he was "willing and happy" to help Mahfouz get a knighthood and citizenship.
Fawcett resigned from his post as chief executive of The Prince’s Foundation back in November.
It all comes as Harry faces paying a huge bill if he loses his High Court battle for security to cover the taxpayer funds that the Home Office has used to fight the case.
Prince Harry launched legal action against the Government over the decision to take away his police bodyguards after he stepped back from royal duties two years ago.
While he wanted to fund his own Met Police armed bodyguards the Home Office refused.
Mahfouz donated £1.5million to Charles’s charities