Ballymena-based property firm, Corbo, has sold the building on Belfast's Donegall Place which is home to the city's main Marks and Spencers shop.
The building has been bought by property investment firm CBRE Investors for £8.75m.
Corbo, which is owned by Sam Morrison, is best known as the the company behind Ballymena's Fairhill Shopping Centre.
Earlier this year it sold the Damolly Retail Park in Newry to a UK investor for £34.9m.
Corbo's chief executive, Stephen Kirkpatrick, said the latest deal signals a growth in confidence in the Northern Ireland property market.
He indicated that the firm was also looking at potential opportunities to buy, which he said will "grow Corbo's portfolio through our dynamic asset management approach and strong financial position".