RTÉ paid Ryan Tubridy 345,000 euro more than declared from 2017 to 2022.
The state broadcaster has described it as a "serious breach of trust".
A review was carried out by Grant Thornton into RTÉ's accounts - which was discussed by the board of the broadcaster on Monday.
It found payments totaling 345,000 euro were paid to Ryan Tubridy between 2017 and 2022 - over what was made public.
The review found RTE had guaranteed additional payments to the former Late Late Show host through commercial partners - in exchange for appearances.
Figures released by the broadcaster show Tubridy was paid in excess of 500,000 euro between 2017 and 2022 - despite his salary being declared below half a million.
Ryan Tubridy stepped down as host of the Late Late Show earlier this year.
The RTE board has apologised
