Businessman Sean Gallagher has settled his case against RTÉ over a tweet read out during a presidential debate in October 2011.
The state broadcaster has agreed to pay him substantial undisclosed damages.
Mr Gallagher had claimed that RTÉ acted unfairly and did not verify the accuracy of the tweet, which came from an unofficial account purporting to be connected to Martin McGuinness.
Today, RTÉ issued an apology acknowledging that it made a mistake broadcasting an unverified tweet and failed to comply with its duties under the Broadcasting Act.
It added that it should have immediately corrected the statement once it realised it was not from Mr McGuinness' account and that it failed to provide subsequent clarification on the matter.
The statement adds: "RTÉ acknowledges that the production of the programme fell significantly short of the standards expected by the public and required by law."
Full text of apology by RTE pic.twitter.com/vCoywr2ek9
— Nicole Gernon (@nicole_gernon) December 19, 2017
Mr Gallagher's solicitor Paul Tweed read out a statement on his behalf afterwards.
He said: "Sean Gallagher is satisfied that RTÉ have, before the High Court today, acknowledged their failure to treat Mr Gallagher with due fairness & impartiality."
Reporting by Nicole Gernon