US Edition The Australian musician and artist made the new recording of the song, which dates from 1902, to mark the 90th anniversary of the end of the Great War.
It tells the story of two brothers who ride wooden horses together as little children before ending up fighting on a battlefield.
In 1969 Harris had one of his unlikely hits with the emotional song which tells of the brothers' loyalty.
It spent six weeks at number one and became the best-selling single of the year.
Now Harris, 78, has re-recorded it with the 60-strong Froncysyllte Male Voice Choir in north Wales.
He told how he discovered the song held a strong resonance for his family because it spoke of what happened to his father Cromwell and younger brother Carl.
In 1911 they emigrated from Wales to Australia aged 16 and 14, before signing up for service in 1914.
Harris told BBC Radio 4: "When the war broke out dad put his age up to 21 so he could vouch that his 16-year-old brother was of military age, which was 18."
On their first military leave together they went to re-visit their family in Cardiff, but their mother was "horrified" that Carl had illegally signed up and tipped-off the Australian authorities which discharged him.
Subsequently he signed up again when he turned 18, joining a different battalion.
Unlike the song, which has a happy ending, Harris said: "They never saw each other again and Carl was killed at the end of the war."
Harris found out about the tragic tale while researching his family's past for a BBC One documentary, My Family at War, which airs on Tuesday night at 9pm.