Property investment company Hibernia REIT will acquire Cumberland House on Fenian Street in Dublin 2 from Morretino for €49m.
As part of the transaction a €38m short-term loan provided by Hibernia to Morretino in August 2014 will be repaid along with close to €1m of accrued interest.
The site covers 1.6 acres and is located in the center of Dublin - close to Trinity College and Pearse Street Dart station.
Hibernia said that Cumberland House has significant redevelopment potential - planning permission has been granted to replace the current building with up to 250,000 sq ft of new office-space.
The property was previously owned by Westmeath developer Christopher Bennett - the building is largely vacant.