It was long known that Derek Quinlan's luxury lifestyle was turning spectacularly sour, but the debts he had left behind in the south of France could only be guessed at. It is there that he owns one of the most expensive holiday home properties across 8,000 sq m of lands with frontage to one of the most expensive private sea views in the world.

The Sunday Tribune revealed for the first time in early October the tens of millions in hugely expensive mortgages facing Quinlan, the former adviser to many of Dublin's professional classes. Now, the mansion, called La Villa Carriere on Cap Ferrat, the exclusive peninsula east of Nice, is officially on sale and Ireland's best-known international property developer can no longer hide his personal losses.

The Sunday Tribune has been told that Quinlan's new lenders, Barclays, which took over the loans from AIB, have been considering action in the French commercial court. Barclays in London refused to comment last week.

This newspaper revealed that public filings in Nice showed the three mortgages of up to €48m that AIB lent Quinlan in 2006, only weeks before the most overheated property boom ever was to burst.

Questions remain about the circumstances in which a credit committee of AIB could forward money in unsecured lending to a property speculator to buy a holiday mansion in the most expensive spot in the world.

The personal loans advanced to Quinlan's fully-owned company then ballooned to almost €65m when he refinanced the AIB loans, at huge expense, at the Monaco branch of Barclays Bank.

Sources on the Cote d'Azur say the property is officially on the market for €80m but it will be lucky to achieve €40m. Property in the south of France, like the top end of the Irish market, is in crisis and now solely depends on Russian oligarchs.

The main villa is not the grandest property on the cape, which boasts some of the finest Belle Epoque mansions in France. Modernised, La Carriere has a large entrance hall, dining room for ten, three bedrooms on the first floor and two on the second floor. The basement includes the obligatory home cinema, a bar and wine cellar. The parkland to the sea is what makes it unique, particularly for owners who value their privacy.

Public filings, as reported by the Sunday Tribune in October, also showed the extent of a planning dispute that had bedevilled the property since planning permission awarded to the previous owner was rescinded by the local mairie in St Jean Cap Ferrat almost a year after its purchase by Quinlan. Quinlan poured in many more millions – one loan from Barclays was worth €8m – to redevelop the property to his taste.

In truth, the property was unofficially on the market ever since Quinlan relocated to Epalinges, a small Swiss town seven kilometres from Lausanne, over a year ago.

Quinlan is described by people who have met him in Cap Ferrat as "very colourful" and as "a nice gentle person if a little bit eccentric".

"There are only maybe 15 properties on the whole of Cap Ferrat like this one with access to the sea," said a local resident. "But for this sort of property it is a market for the Russian oligarch only. The French do not buy because they have more sense and they do not have the money."

Cap Ferrat is one of the most sought-after spots in the world.

"It must be an over-used expression but it must be one of the most attractive pieces of real estate," said a property adviser last week. "But in 2006, La Carriere would have fetched in this state €80m. A record of over €100m was paid on Cap Ferrat. It would be lucky to fetch €40m now," he said.

That valuation suggests that Quinlan faces about €20m in losses on the capital loans alone, not including the huge interest costs and the local tax bills.

The financing of Cap Ferrat

January 2006: Quinlan buys La Carriere and its 8,000 sq m of lands through his 99.9%-controlled company, financed with a primary two-year mortgage of €30m from AIB. The property consists of the main villa, housekeeper's residence, garage with pigeon loft, pavilion, greenhouse, swimming pool, extensive parklands and pleasure gardens that stretch down to the sea.

February 2006: AIB registers the mortgage office in Nice.

December 2006: Planners refuse to transfer existing permission, granted two years earlier to the previous owner. Company documents do not say why the licence was revoked.

September 2007: AIB advances Quinlan €8m in another "conventional" 10-year mortgage.

July 2008: AIB lends another €10m over nine years. AIB's total mortgages on the property have ballooned to €48m, according to public records.

2008: Quinlan starts to refinance the property with three loans from the Monaco branch of Barclays Bank. By last year, mortgages and other liabilities held by the company that controls La Carriere totalled almost €64m.

April 2009: Quinlan takes full control of the company linked to the estate. Public filings show Barclays refinanced the property, with three loans to Quinlan totalling over €56.25m. The Quinlan company faces a further €9.9m liability from money in an account that has not been reimbursed at the end of 2007. Quinlan agrees to pay Barclays 6.4% interest for the main €48m loan. A second loan for €8m, earmarked for development work on the estate, is a margin above the euro overnight bank rate, an effective annual interest rate of 5.7%. The third loan from Barclays of €280,000, earmarked to pay the expenses in raising the first two loans, has an effective annual rate of 8.39%.

April 2009: La Carriere is valued on the company's books at €65m.

2010: Quinlan faces an annual 3% property tax based on market value, suggesting a tax bill of €2m a year.