It was held to mark the forty days since the ex-king’s funeral and burial, which were also held in Athens.
His sisters Sofia and Irini arrived at the cathedral shortly before 11:00, followed a short while later by his widow Anne-Marie, his sons Pavlos, Nikolaos and Phillipos, and his daughters Alexia and Theodora, accompanied by their spouses.
Close friends and schoolmates of the former king attended the service, alongside personalities from the spectra of business and politics.
Following the memorial service, family and guests were expected to attend a lunch gathering at the Stavros Niarchos Foundation.
Another church service and the unveiling of Constantine’s tomb will be held on Sunday, at the former royal estate of Tatoi on the outskirts of Athens, where his body is buried in the family’s cemetery, alongside his ancestors.