George Best Belfast City Airport has been sold as part of a package of UK and European assets. EISER Finance Ltd is selling the assets to 3i funds, managed by 3i Investments plc.
It's understood the sale will have no impact on the day-to-day running of the airport.
There was no comment from the airport on the deal. But it's understood management are hoping for investment from its new owners - with improvements to its car park top of the list.
EISER bought the airport for £132.5m in 2008, and is thought to have spent around £20m on improvements to the airport over the last eight years.
As well as George Best Belfast City Airport, the deal also includes gas transporter and electricity network East Surrey Pipelines.
EISER Global Infrastructure Fund (EGIF) is also selling assets in Italy and Spain to 3i as part of the deal, which is worth hundreds millions of pounds.
Reports earlier this year suggested that 3i could pay as much as €600m (£509.5m) for the package. The proposed sale was first revealed in the Belfast Telegraph in April but has only now been finalised. Economist John Simpson described the sale of the airport as an "investor decision" by its one-time owners. And he said he believed the performance of the airport may have disappointed EISER.
"They did expect it to increase its turnover and profit a little bit more if restrictions on the City Airport were lifted - but of course, that hasn't happened."
The number of departure seats which the airport can sell in a year is currently capped at two million.
In its accounts for 2015, the airport reported operating profits, before exceptional items, of £3.3m, up from £2.4m. Revenue was up around 5% to £20.8m.
This week, the airport was coping with the Christmas rush of passengers, with around 10,000 people expected to come and go every day this week. Speaking earlier this week, airport commercial and marketing manager, Katy Best, said 2016 had been a "successful" year.
Developments included a new three-times weekly link to Reykjavik with Icelandair, starting in June. It also announced a new ski route to Salzburg, Austria in November.
EISER took control of ABN AMRO - which had bought the airport from former Spanish owners Ferrovial Group. Ferrovial had paid £35m for the airport in 2003.
The sale is the latest in a string of big deals affecting Northern Ireland businesses this year.
This week, Thompson Aero Seating was sold to Chinese state-owned business AVIC.
The first six months of the year also saw the sale of TV broadcaster UTV Ltd to ITV and the sale of the radio stations in UTV Media plc, which rebranded as Wireless Group, to News Corp.