Caldey Abbey in Wales has apologised for historical child sex abuse perpetrated by a monk between the 1960s and 1990s.
The review, led by social worker Jan Pickles, detailed horrific abuse by Fr Thaddeus Kotik across decades at the Cistercian abbey and the surrounding island, which lies off the Pembrokeshire coast.
It describes how Fr Thaddeus used gifts and "special attention" to "groom" children and their parents into trusting him.
Fr Thaddeus would "exploit his status as a monk" by offering families babysitting or guided tours, and use a pet tortoise and "other attractive treats" to lure children to secluded to spots around the abbey or island where they were then abused.
Even when there were suspicions around his behaviour, leaders failed to act or remove him from the island.
"It appears that these behaviours were 'common knowledge' within the island communities and tolerated," the report said.
Fr Thaddeus died in 1992 without ever being held accountable or brought to justice for his actions.
"There appears to have been a failure of leadership at the highest level within the Order and Abbey. Serious matters of repeated and frequent allegations of child sexual abuse by [Fr Thaddeus] were not reported to the statutory authorities as the law of that time required," the report said.
Victim testimonies suggested that Fr Thaddeus was a "serial and prolific abuser of children, often in 'plain sight' of others".
"[Fr Thaddeus'] interest in children was not hidden from view, and it appears to have been tolerated by adults on the Island," it stated.
The review found that victims were often not believed and in one instance, a child who reported the abuse to their priest was told "he would suffer terrible punishment and be sent to Hell" if he shared what had happened with anyone else.
The review concluded that the abbey had "weak oversight and governance arrangements relating to safeguarding on the Island", and had failed to properly investigate complaints, even becoming "adversarial" towards victims.
"The allegations were never reported to the statutory agencies responsible for protecting children. The Reviewer believes that these were missed opportunities," it added.
The report recommended the introduction of stringent safeguarding policies and procedures, including "a clear 'No Touch' policy" and a ban on all pastoral counselling and informal contact between monks and visitors to the island.
Abbot Fr Jan Rossey, who commissioned the review, apologised for the abbey's failure to protect children, and expressed "deep sorrow and regret" for the suffering experienced by Fr Thaddeus' victims.
"It is particularly heartbreaking to hear children spoke up to adults and no action was taken. Children and their families were failed when they should have been supported and listened to," he said.
