Sheikh Mansour bin Zayed Al Nahyan - the owner of Manchester City football club, who pumped £3.5 billion into Barclays as part of a wider capital-raising by the bank to shore up its balance sheet in 2008 - sold his 7% stake last month.
The move will have generated a hefty profit for the Middle Eastern investor, given that the lender's share price has rocketed by more than 60% since the deal in October 2008.
Former Barclays boss Bob Diamond - who quit last year in the wake of the bank's Libor rate-rigging scandal - secured the investment nearly five years ago, with sovereign wealth funds in Qatar and Abu Dhabi injecting a combined £7.3 billion into the group to save Barclays from the fate suffered by part-nationalised groups Royal Bank of Scotland and Lloyds Banking Group.
The investors were given discounted access to stock and investments that could be converted into additional shares at a later stage.
But the capital injections have not been without controversy, with the Serious Fraud Office (SFO) last year launching an investigation into the fees paid by Barclays in connection with its Qatari fundraising.
The group has been embroiled in scandal for the past year, only this week seeing United States regulators uphold fines of 453 million dollars (£300 million) against it and four traders for alleged power price-fixing.
Barclays has vowed to "vigorously defend" the accusations and fines, but it adds pressure as the group is already battling to repair its image in the wake of its £290 million Libor-rigging settlement last summer.
The bank's new boss Antony Jenkins has since led a crusade to overhaul the culture at the bank, telling staff to adhere to a new set of values or quit.