It is understood the investigation was launched when people living in the area noticed inappropriate behaviour between the two.
Without the intervention by neighbours "the case may never have come to light let alone end up in a prosecution" the source added.
"This case highlights the level of engagement between gardai and other countries in these cases and shows that international borders don't hinder an investigation like this."
During the investigation it emerged that he convinced the young girl they were in a legitimate relationship and told her he wanted “100 kids”.
When in Ireland the pair stayed in hotels, a campsite and a holiday home.
Neighbours living near the holiday home in an Irish seaside down alerted gardai when they became suspicious about the level of affection between the two.
It is understood Tremblay told gardai initially he was the girl’s father.
Edmonton Law Courts in Alberta heard details of how Tremblay preyed on the vulnerable teen who had recently lost her mother.
He sent her naked images and encouraged her to reciprocate.
The girl told her father she was staying with a friend during Tremblay’s visits.
When her dad read an excerpt from a letter he had sent the victim and became concerned Tremblay lied about his age and promised to cease contact.
He continued the relationship however and returned to Ireland for a second time.
In a victim impact statement the girl’s father revealed the stress induced by the incident for the family and said his daughter had been brainwashed by Tremblay.