Nelson, who have run the Ally Pally fixture in north London since 2008, will hold their last outing there on May 11.
The move comes after Blair Barrows, son of Nelson's founder Peter Barrows, decided to return to full-time university studies. He is based in Edinburgh, while his father is based in Newmarket and director Paul Kelly in London.
"The reduction in our management team means that we are unable to give this fair the focus it requires to maintain its ongoing success," Peter Barrows told ATG. "This flagship fair for the trade couldn't have gone to a better company to whom I give every support. I believe that IACF are the only organisers who can realise its potential."
Keith Harris, chairman of IACF, expressed himself delighted to have "this jewel of London events" added to his company's portfolio - he had tried to buy the fair in 1994.
"We will ensure that the resources required to develop and grow Alexandra Palace will be put in place," he said.
These resources include the antiques and collectors' fairs rental at Ally Pally: "not much cheaper than hiring Olympia", said Mr Harris.
Lindy Berkman and Alan Kipping ran the antiques and collectors' fair at Ally Pally under the Pig and Whistle Promotions' banner from 1981-88. In 1986, Mr Kipping launched his own antiques and collectors' fair at Sandown Park Racecourse.
From 1988 to 2006 Ms Berkman ran the Ally Pally fair herself still under the Pig and Whistle name. Exhibitor numbers peaked at 750 during this period, with long waiting lists, something which IACF will surely seek to emulate.
The acquisition of this popular and long-running event, held four times a year and one of the few remaining Sunday fairs, now fields 300-400 standholders.
The closest to London that IACF, who now field 29 fairs at five UK locations which see 60,000 trade buyers annually, have come before is an antiques and collectors' fair they ran from 2011/12 at the Hertfordshire County Showground, near St Albans.
Peter Barrows founded Nelson Events in 1999, with his first antiques fair and collectors' fair at Greshams School at Holt in Norfolk, followed in 2002 by one at Newmarket Racecourse. Last year the organisers launched a new fair in Kettering, Northamptonshire. These three well-supported fairs remain in the Nelson Events portfolio.
Announcements will shortly appear on both organisers' websites and members of IACF's team will be at Nelson Events' last fair at Alexandra Palace on Sunday, May 11. The first IACF event at Ally Pally will be held on Sunday, September 14.