Arlene Foster, the first minister of Northern Ireland, has told a court she was humiliated by unfounded allegations of an affair with a protection officer. The Democratic Unionist party leader is suing the TV doctor Christian Jessen for tweeting what was described in court as an unsubstantiated rumour of an extramarital relationship. She told the high court in Belfast on Wednesday it was a personal attack that sought to destabilise her at a politically fraught moment. 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, a presenter on the Channel 4 show Embarrassing Bodies, sent the initial tweet on 23 December 2019. It was retweeted more than 500 times and the court heard he had followed up with other “aggravating” tweets. He had more than 300,000 Twitter followers. He was described in court as a medical doctor who practises as a GP on Harley Street in London. The DUP leader, who represents Fermanagh and South Tyrone in the Stormont assembly, said it was “very upsetting” to explain the unfounded allegation to her husband and that there was little sleep in her home that night. After complaints from Foster, Jessen deleted the original tweet on 7 January 2020 but did not apologise. The court was told 13 emails and letters to the TV presenter had gone unanswered. He was not represented in court. Foster said the allegation had come while she was involved in talks to revive Northern Ireland’s power-sharing government, which had been mothballed for three years. She said the rumour had surfaced online from anonymous accounts before Jessen’s tweet. “I think the attack on me personally and my marriage was meant to destabilise me at a very critical time,” she told the court. 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.” Foster told the court she was not homophobic. “I do get distressed when people call me a homophobe because that’s something I am not,” she said. “I do think, unfortunately, in politics sometimes, if you take a nuanced position on one issue it becomes a much wider piece, and that’s unfortunately the case – if you cannot explain it in 140 characters in today’s society then it must be true – it is simply not true. “I have many friends who are homosexual, they know my views on same-sex marriage, and in any event, same-sex marriage is now the law here in Northern Ireland and has to be upheld. I have never in my own political utterances said anything in connection with people who are homosexual and that’s why I do get quite upset when people call me a homophobe.” Mr Justice McAlinden said he would reserve his decision and make a written judgment.