My husband Earl Spencer kept a long-term mistress and dumped me by text: Estranged wife's astonishing court claims about end of her marriage - and the explosive email she sent to his archaeologist girlfriend

Princess Diana's brother kept a 'long-term mistress' before dumping his 'helpless and confused' wife by text message, court papers allege.

Earl Spencer then 'completely refused' to give any explanation to Countess Karen Spencer which she found 'both cruel and inexplicable'.

She is accusing her husband of having had an affair since 2022 'and more likely since 2021' with Dr Cat Jarman, an archaeologist digging for a Roman villa at his Althorp ancestral home where he grew up with Diana.

High Court papers reveal an email the 'shocked and devastated' Countess Spencer wrote to her husband's girlfriend saying: 'First of all as a woman, I just have to tell you that I am so disappointed in you. Turning all of the children's lives upside down like this is so unbelievably immoral.'

She signed off her message in May this year by saying: 'Good luck Cat, you're in for a hell of a ride. I think that you'll find having him to deal with full-time will be much trickier than the odd five-day escape to Norfolk and a night or two in London here and there.'

The allegations form part of Countess Spencer's defence to an explosive High Court privacy case brought against her by Dr Jarman.

The 60-year-old earl's archaeologist girlfriend, 42, is suing his estranged wife, 52, accusing her of revealing private details of her life.

Earl Spencer tonight said his estranged wife's claims were an 'absurd attempt to blacken my name', while Dr Jarman said she was 'shocked and utterly dismayed' and accused the Countess of mounting a 'hideous and defamatory attack' on her.

'I can understand that she finds it difficult because he moved on before she did, but the narrative that Charles, or I, did something wrong here is simply not true.

'I do have sympathy for her. I understand what she has lost, because it is more than her marriage and her home. But this still doesn't justify what she did.'

But in her defence, Countess Spencer says her disclosures were 'entirely justified and legitimate' given the way she was treated.

The Canadian-born social entrepreneur became Spencer's third wife in 2011, and they have an 11-year-old daughter, Lady Charlotte Diana. 

She was informed by the earl on March 19 this year that 'their marriage was over after almost 13 years. 

He did this by text message', her defence papers say, adding: 'Having given up her life in the United States, in order to live in the middle of rural Northamptonshire and dedicate herself to sorting out the Althorp Estate business, as well having a child, the news was hideous for Lady Spencer.'

When Countess Spencer compared notes with Dr Jarman's husband, Tom Jarman, 'she discovered that their affair had been going on since at least November/December 2022 when the two of them were together in Norfolk (although more likely since 2021)', the defence states.

During the dig, the archaeologist and her team had been staying on the Althorp estate and dining at the house.

In her email to Dr Jarman, the countess wrote: 'Not sure what Charles has shared with you of this, but I won't have you at Althorp while I still live here. That is a boundary I intend to hold. It's not fair to me, our daughter, or to all the staff, who are already distraught at the news of our divorce though having to serve Charles' long-term mistress. It's just too much to ask.'

The earl – who has been married three times and has had a well-documented colourful love life - and the countess announced their split in June, and he publicly confirmed his relationship with Dr Jarman in October.

In his girlfriend's legal claim against his wife – they remain married pending a divorce – she alleges that she was shocked when the countess revealed her private information to him.

In her Mail interview, Dr Jarman said: 'I have worked very hard indeed to keep my MS hidden, as should be my prerogative. So only a handful of people have known – and Charles wasn't one of them. 

'I'd been seeing him, romantically, for only two months or three months, and still hadn't told him. It's hard, isn't it, knowing when you reveal something like that.

'Some people do from the off, but I chose not to. And I stress that it was my choice. Your medical history is the most private thing.'

She alleges that Spencer's wife 'found out from someone close to me' and 'in the course of a conversation about whether I had been having an affair with her husband – which I can categorically say I had not been, we were very much just friends and colleagues until after the marriage had ended – Karen learned that I have MS.

'It was also confirmed to her that this was not something that was widely known. And yet she then went to Charles and said: 'You do know she has MS, don't you?'.'

The legal action is at an early stage and has not yet come to trial.

Countess Spencer is fighting the case, and her defence papers state: 'For the avoidance of any doubt, Lady Spencer is perfectly entitled to and will (where relevant or necessary) continue to explain that [Dr Jarman] and her husband had an affair and that this was why he wanted a divorce and offered no explanation for doing so in such an insensitive and inexplicable manner after 13 years of marriage.'

Countess Spencer has repeatedly refused to comment on the breakdown of her marriage and the ensuing legal action against her.

Friends say she wants to fight the case in the court, through publicly available documents and evidence.

Last night Dr Jarman said: 'I am shocked and utterly dismayed that my rightful attempt to stop the unlawful dissemination of my status as a person with Multiple Sclerosis - a protected disability - has been hijacked in such an appallingly untruthful way.

'It seems that Karen Spencer is not so much mounting a legal defence to my legitimate action, but has rather stooped to make a hideous and defamatory attack on Charles and me.

'In the meantime, the stress of this matter, which could have been resolved by Karen Spencer in a few minutes many months ago, further seriously impacts my health. Stress is a well-known driver of MS.

'My full response to this outrage will be with the Courts at the earliest possible opportunity, and at the same time we are urgently looking at all available legal redress, including that relating to the breaking of legally binding oaths.'

Earl Spencer added: 'The notion that I would end my marriage by text is an absurd attempt to blacken my name. Karen ended the marriage, after endless threats to do so over the years, in early March.

'She asked me to confirm the end of the marriage in a text of 18 March and my reply that day was a simple acceptance of her decision. I have those texts still, and will share them in court when I clear my name.'