Rothschild’s family is reported to be ”worried sick’’ about her new relationship. ”Her mother and all her family are very concerned that Kate is going off the rails,’’ another source said. ”Kate and Alice are talking, but most of the family are not on speaking terms with her at the moment. The whole situation is very sad.’’

So just how did this union descend into a debacle worthy of the Jeremy Kyle show?

Rothschild, who began her relationship with Goldsmith when she was 17, has been enjoying rather different interests of late to the family’s usual society pursuits. Her fledgling music career with Roundtable Records led to an ”increasingly nocturnal’’ lifestyle. Her husband’s fears were realised when, a friend says, he “found texts and email messages” between Rothschild and Jay Electronica, who is one of her clients. Worse still, “they were very intense messages planning sexual liaisons”. The “passionate” affair had reportedly been going on for a year. In the confrontation that followed, 31-year-old Goldsmith was arrested at the couple’s £20 million home in Kensington, on suspicion of actual bodily harm. He was said to have slapped his wife and kicked a toy at her, at which point she called the police. He was released without charge after accepting a caution, before taking their three children on holiday with his mother, Lady Annabel.

That, aside from the lawyers’ fees, could have been that, but for the couple taking to Twitter – an extraordinary act for a family that values privacy as much as the Goldsmiths do. Rothschild, 29, claimed she had been cheated on ”several times’’ and even posted a picture of the children, Iris, eight, Frankie, seven, and Isaac, four, being returned to her on a private jet, alongside a series of bitter and increasingly hysterical posts.

Goldsmith branded her behaviour ”appalling’’ and lapped up commiserating messages from the Twitterati. After reports that she had hired a PR firm to manage the crisis, he posted: ”A bit late surely? How about focusing on her devastated children?’’

Ten years ago, Goldsmith was named Britain’s most eligible bachelor by Tatler. Known as Ben-Ben by his family and born when his mother was 46, Goldsmith provided solace for Lady Annabel when her first-born son, Rupert [by first husband Mark Birley], disappeared off the coast of West Africa while swimming in 1986.

Kate comes from an equally illustrious line, her father from the Rothschild banking clan, and her mother from the reputedly cursed Guinness brewing heirs. She grew up at the family pile, Rushbrooke Hall, Bury St Edmunds and went to school at Bryanston, Dorset, where she had a reputation as a “party animal”.

It would be easier for a camel to pass through the eye of a needle than to deem whether Goldsmith or Rothschild is richer. Goldsmith’s money is tied up in family trusts, which are so convoluted that his father boasted they could never be unravelled. When Sir James died, he left assets worth about £1.2 billion and each of his children was estimated to have received £10 million in spending money. The founder of a green investment business, Goldsmith is said to be now worth £300 million. He has invested in the concierge business quintessentially.com, set up by Ben Elliot, nephew of the Duchess of Cornwall. He also backed Marco Pierre White’s private dining club, Drones.

For her part, Rothschild shared an £18 million inheritance when her father, Amschel, killed himself in a Paris hotel room in 1996 at the age of 41. He had joined the family firm only nine years before, taking his place in what has been described as ”the closest thing to a Jewish Royal Family in exile’’. The half brother of Lord (Jacob) Rothschild, he was being groomed to take over the family bank, NM Rothschild, from his second cousin Sir Evelyn de Rothschild. He was found hanged after a business meeting, and his death, when Kate was 14, remains unexplained.

Rothschild is expected to gain custody of the couple’s children, unless her husband can prove that she is an unfit mother. The pair will divide the proceeds of the family home, bought for £5 million in June 2002, through a company registered in the British Virgin Islands.

Two days ago, Rothschild posted emotional late-night tweets: ”To all the vultures harassing and taunting me, the people calling me a whore and a bad mother, the threatening emailers and callers: I have been with my husband since I was 17, my whole life from then until now has been dedicated to him and our children. Ben in a rational mood would be the first to say that my devotion to my children is unshakeable. I am with them now, as I always am.