A stately pile and surrounding lands in Co Antrim bought by the firm owned by medical millionaire Peter FitzGerald went for well over the £5m asking price, sources have revealed.
It is thought that the sale is one of the largest private property sales made anywhere on the island of Ireland this year.
And it was the single largest transaction in Northern Ireland this year "by a considerable margin", according to Tughans law firm, which announced the acquisition.
The Bushmills estate includes 350 acres earmarked for a £100m 18-hole championship golf course, luxury five-star 120-bedroom hotel and 70 golf lodges.
The total package is around 1,200 acres and includes Dundarave House, a 19th century stately home with 19 bedrooms, a farm and shooting business.
The deal also includes the Port Moon estate, once home to a salmon fishery.
In July the businessman behind the proposed golf resort, Dr Alistair Hanna, died.
The estate - once ancestral home of the Macnaghten clan - and surrounding lands have now been bought by subsidiaries of Randox, the Crumlin-based medical testing company started by Dr FitzGerald in a hen-house on the family farm.
Neal Morrison of Savills Belfast, which handled the sale, said that the deal was completed less than six months after Dundarave went on the market.
"We expect demand for similar properties to remain strong in 2015," he said.
James Walker of Savills UK added that Dundarave attracted significant global interest. "We are all delighted that the prosperity of the estate will be secure for the foreseeable future," he said.
Tughans said that the new owners were currently considering their options over the existing planning consent, although there was speculation last month that polo fan Dr FitzGerald would dedicate some of the land to his favourite sport.
David Jones, a partner at Tughans, said the transaction was "unique in Northern Ireland".
Now all eyes are on Drenagh Estate in Limavady, which has been the home of the McCauslands since around the 19th century.
It is understood that the house and 1,000-acre estate are on offer for around £10m with Simon Brien Residential.