Anglo lent Clarendon – co-owned by McKillen and Tony Leonard – around $135m to buy the building in 2006.

The purchase price was around $170m.

Most of McKillen’s loans to Anglo were bought out by US private equity group Colony Capital as part of the sale of the Project Pebble portfolio last year. “Everything is paid off and gone and out of Anglo. This is the end of it,” according to one source.

“Paddy McKillen’s business model has always been consistent. He buys quality assets that produce income which more than finances the borrowings. He then improves the asset and holds it for the long term. He doesn’t buy things just to resell them,” said a property source.

McKillen targets investments that produce income one-third higher, after costs, than borrowing charges. During his 2010 High Court case over Nama, it emerged that McKillen’s rent roll was 1.7 times the size of his borrowings.

The Boston building at Franklin Street is one of a number of prime real estate assets in the Belfast-born property investor’s portfolio. Other blue chip assets include a major stake in the world-famous Claridge’s, Berkeley and Connaught hotels in London, the Jervis Street Shopping Centre in Dublin and the Chateau La Coste vineyard in the south of France.

McKillen’s final exit from his Anglo bank debts is the latest in a series of high profile property magnates leaving the clutches of state banks or Nama. A phalanx of private equity groups, hedge funds or specialist finance houses have been jostling to buy property backed loans from Nama and the banks which have been deleveraging at a ferocious rate.

Bill Durkan’s UK-based Durkan Group was one of the first to exit Nama when it paid off close to €40m worth of loans that had transferred to the State’s bad bank. It described dealing with Nama as “unsatisfactory”.

Michael O’Flynn, who developed the Elysian in Cork, Ireland’s tallest building, has also left the Nama shackles, as the Project Tower portfolio of loans associated with his assets in Ireland, UK and Germany was bought by Blackstone Real estate Partners Europe last month.

Ballymore Properties’ Sean Mulryan has hired Lazard and CBRE to help its secure joint venture funding for its €2.5bn “Mini Manhattan” project at Nine Elms in London.

The proceeds from this ambitious scheme will be used to pay down Ballymore’s debt held by Nama.