Organisers of the Belfast City Marathon have apologised to nearly 18,000 runners who took part after informing them they ran the wrong distance.
A statement said there had been a "discrepancy" with the 26.2 mile route length.
The statement, on the Deep River Rock Belfast City Marathon website said: "A full review will be conducted and feedback gathered from all partners involved.
"The Event Organisers wish to congratulate everyone on their run today and appreciate the disappointment of some. They wish to extend their apologies to all impacted."
The event's course measurer, John Glover, later said runners had twice been" taken off the measured route".
The BBC reported he said: "The route run was 469 metres in excess of the route measured and approved by the Association of International Marathons."
The event's organising committee chairman David Seaton told the BBC there had been "a problem" during the race.
He said: "We're holding our hands up and we're addressing it. We wish it hadn't happened.
"It was a new course and there were lots of things to take in consideration including new legislation which we had to work around."
