The Church in Wales was made aware of a complaint about priest Anthony Pierce's conduct against a person believed to be under the age of 18, in 1993.
He was later elected as Bishop of Swansea and Brecon in 1999 and served until 2008.
In a letter to the Diocses, the current Bishop of Swansea and Brecon, John Lomas said, "We know that in 1993 another discourse was made in relation to the conduct of Anthony Pierce".
The allegation against Pierce was reported to police 17 years later, in 2010.
However, South Wales Police were unable to investigate the claims because the alleged victim had died.
This allegation has come to light after Pierce pleaded guilty in February of this year to multiple counts of sexually abusing a child at Swansea Crown Court, in a separate case.
The Church in Wales has launched a review into Pierce's appointment, which it says "seeks to establish who within the Church received relevant information, and what they did with it."
In early February 2025, Anthony Pierce pleaded guilty at Swansea Crown Court to abuse in the 1980s whilst he was a parish priest in the West Cross area of Swansea.
Pierce, who was the Bishop between 1999 and 2008, pleaded guilty to five counts of indecent assault on a boy under 16 years of age when he appeared at Swansea Crown Court.
Since then, it has emerged the Church was aware of a separate allegation of abuse against him made in 1993.
The allegation was passed to South Wales Police in 2010, seventeen years after it was made.
In a statement, the force said, "Sadly, in this specific case the victim had passed away in 2010 when allegations were made of abuse taking place in 1993.
"Therefore we are not able to progress the investigation”.
The Church in Wales has launched a review into "the handling of an allegation of abuse against the Right Reverend Anthony Pierce, first reported in 1993."
The Chair of the Church in Wales Safeguarding Committee has appointed an "independent lay person" to carry out the review.
It added, "The Reviewer is not asked to review matters concerning an allegation against Mr Pierce reported to the Church in Wales Safeguarding Team and South Wales Police in 2023."