Anthony Arlidge QC, 76, was called "bonkers" by his partner of 12 years, Constance Briscoe, 55, for announcing that he was leaving her for the 25-year-old paralegal.
She claimed that Mr Arlidge and his new girlfriend, Heather Lockwood, an aspiring barrister, were both "intelligent people" but the situation was "ridiculous". Mr Arlidge, who has nine grandchildren, has hit back, saying they are "very happy" together and the relationship even has the support of Miss Lockwood's mother, Jacqueline, 54.
Despite being more than three times the age of his lover, the QC said: "I've met her mother and she says if her daughter is happy then so is she."
Miss Lockwood, who was born in Durham, was called to the Bar at the Middle Temple two years ago but has yet to get herself a pupillage. Friends say she is "a normal girl" who loves sports. She works for Watmores Solicitors in Chancery Lane, central London, near the flat she shares with Mr Arlidge. The pair are said to have met in September at a dinner in Middle Temple, where she was a student and he was Master of Entertainments for 20 years. She was looking for a placement with barristers at the time.
A former Crown Court recorder and father of four, Mr Arlidge moved out of Miss Briscoe's £1 million house in Clapham, south London, after ending their relationship.
The mother of two, Britain's most successful black judge, said: "I was shocked and upset but have not fallen out.
"They're both very intelligent people but I think it's bonkers."
Miss Briscoe said she could not comment on Miss Lockwood's motives. "It is true that it is hard to get a pupillage and it is becoming even harder these days," she said.
"It really is a cat fight out there and of course contacts have always helped.
"Tony is too old for a mid-life crisis. It is hilarious. I don't know what she wants or what she is trying to do but good luck to them. Tony was giving a speech at my daughter's birthday party. He told me just before we left to go there that he had fallen in love with this girl. I was very upset, but that's life."
Judge Briscoe, a mother of two, is likely to take the separation in her stride.
After working in a number of jobs to get through university she was called to the Bar in 1983, and in 1996 became a recorder, a part-time judge, one of the first black women to sit as a judge in Britain. She is known for her books, Ugly and Beyond Ugly, which were based on the neglect and cruelty she claims to have overcome during her upbringing,
She also talks about her experiences publicly.
Mr Arlidge, whose cases have included the Jeremy Bamber murder trial, works part-time at 18 Red Lion Court chambers, which has offices in central London and Chelmsford, Essex. He remains married to Enid, the mother of his four children.
Their 48th wedding anniversary is next week but they separated nearly three decades ago.
