The celebrity doctor Christian Jessen has been ordered to pay £125,000 in damages to the Northern Ireland first minister, Arlene Foster, for a tweet that falsely claimed she was having an affair. The high court in Belfast awarded the sum – a record for a case hinging on a tweet – on Thursday to vindicate and compensate Foster, the outgoing leader of the Democratic Unionist party (DUP), for what it said was a baseless accusation. “It was an outrageous libel concerning an individual of considerable standing, attacking her integrity at a most fundamental level and it involves the trashing, in a very public fashion, of the relationship that Mrs Foster holds dearest in her life,” said Mr Justice McAlinden. “It affected core aspects of the plaintiff’s life, namely, her relationship with her husband and her deep Christian faith.” Jessen was also ordered to pay Foster’s legal costs. The court heard that Jessen, a presenter on the Channel 4 show Embarrassing Bodies, sent the initial tweet, repeating a false rumour that Foster was having an affair with a protection officer, on 23 December 2019. He had more than 300,000 Twitter followers. It was retweeted more than 500 times and liked by more than 3,500 Twitter users. When a solicitor for Foster contacted Jessen via Twitter, the court heard he responded with other “aggravating” tweets, including “lol”. Jessen deleted the original tweet on 7 January 2020 but did not apologise. “I don’t think Dr Jessen will be laughing this morning,” Foster’s solicitor, Paul Tweed, said outside the court. The victory marked a bittersweet day for Foster, who is to formally cede leadership of the DUP later on Thursday to Edwin Poots, a rival who led a revolt against her last month. In an earlier hearing Foster told the court the tweet was a personal attack that sought to destabilise her during talks to revive power sharing at Stormont. She said she had to have an “upsetting” conversation with her husband. “It was very humiliating to see that the relationship that’s most important to me had been trashed, if you like, and put out there in the public domain in that fashion. One of the things that gives me stability is my home relationship – it was almost as if this cut to the very core of my life.” The court heard that Jessen’s tweet had referred to Foster as “the sanctity of marriage preaching woman”, a reference to the DUP leader’s opposition to same-sex marriage. “It always comes back to bite them on the arse in the end.” • This article was amended on 28 May 2021 to clarify that the sum awarded to Foster was a record for a case hinging on a tweet, not for all libel damages.