Tom Lutton, from the Wirral, was part of an amateur cine group making a film at the castle almost 50 years ago when he agreed to take a photo of eight youngsters playing nearby.
Mr Lutton kept the photograph - along with others from that time - in a box for years, unseen by more than a handful of people.
In April he returned to Flint Castle for the first time since 1965. While he was there, he asked nearby residents if they knew any of the subjects in the photograph - to no avail.
A week later he got in touch with ITV Cymru Wales to appeal for help in reuniting the group and to give each member a copy of the photograph.
Mrs Smith, who in the original picture can be seen sitting on the wall at the back on the left, knew at least five members of the group who still lived in Flintshire.
ITV put Mr Lutton and Mrs Smith in contact and together they began the tricky process of trying to organise a group reunion to recreate the photograph.
One member, Desmond Dundon from Gloucestershire, now lives in Abu Dhabi but fortuitously was able to make it back to Flint for the second photograph.
Sadly one member could not be present for the reunion.
Mr Lutton describes the story behind his chance black-and-white snapshot as 'remarkable'.
He said: "There is so very much in each and every one of those expressions."