The billionaire Abu Dhabi sheikh who bought football club Manchester City two months ago is set to pump up to £5 billion into Barclays.
The bank unveiled Sheikh Mansour Bin Zayed Al Nahyan, a member of the country's royal family, as a major investor in plans to raise up to £7.3 billion to strengthen its finances.
Two other existing Middle East investors - the Qatari Investment Authority and Challenger, which represents Qatar's royal family - are also putting up more funds.
The trio could own nearly a third of the bank between them following the capital-raising exercise, with Al Nahyan's stake in Barclays a potential 16.3%.
The sheikh's billions helped lure Brazilian star Robinho to the Premiership football club for a British record £32.5 million in the summer. Now Barclays hopes his wealth will help it meet the tougher capital requirements called for by the Financial Services Authority to enable banks to withstand financial turmoil.
The Middle East cash helps Barclays shore up its finances without using public funds - meaning that the bank will be able to pay dividends to its shareholders, unlike Royal Bank of Scotland and Halifax Bank of Scotland.
The cash will boost its core tier one ratio - a key measure of capital strength - to 7.6% from 6.3% in July, the bank said. It follows a £4.5 billion fundraising exercise earlier this year.
Chief executive John Varley said: "Today's capital raising provides certainty and speed of execution."
The bank chief said the growing presence of Middle Eastern investors reflected the "significant shift" in the availability of capital and economic power over the past five years.
Mr Varley called the move - which has to be approved by shareholders - a "forward-looking and progressive approach to managing the share register".
