Ryan Tubridy stepped down as host of the Late Late Show earlier this year.
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 RTÉ 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 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 RTÉ board has apologised
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