Charles Saatchi has told a court he does not know if he believes allegations his ex-wife Nigella Lawson was a habitual drug user.
Speaking at Isleworth Crown Court, the art dealer said he was "utterly bereft" that a private email he sent the celebrity chef referring to her being "off her head" on drugs has been made public.
"If you ask me whether I actually knew whether Nigella ever took drugs, the answer is no," Mr Saatchi added as he gave evidence in west London, where his two former personal assistants are on trial accused of fraud.
Italian sisters Elisabetta and Francesca Grillo allegedly used credit cards loaned to them by the celebrity couple to spend more than £685,000 on holidays and luxury items.
Questioned about the email by prosecutor Jane Carpenter, Mr Saatchi said: "I'm utterly bereft that this private email to Nigella has come back to haunt us both. That's all I have to say.
"The stories that the Grillos were parading was that Nigella had a severe cocaine habit that stretched back a very long time for the entirety of our marriage.
Elisabetta and Francesca Grillo deny the allegations against them"What I was speculating here was that the Grillos would use this as a defence."
Sky's senior news correspondent Ian Woods, outside court, reported that Mr Saatchi said he had never seen any evidence that Ms Lawson used drugs but that he had questioned other members of the household about whether the allegations were true.
Mr Saatchi later said: "I have never, never seen any evidence of Nigella taking any drug whatsoever.
"I want to be helpful, but I genuinely have no real knowledge at all."
The couple went through a high-profile divorce earlier this year and Mr Saatchi told the court he was "heartbroken to have lost Nigella".
"I wish the last year had never happened," he added.
The defence barrister handed Mr Saatchi photos from outside Scott's restaurant in Mayfair, where he appeared to have his hands on Ms Lawson's neck.
He said: "I was not gripping, strangling or throttling her. I was holding her head by the neck to make her focus, can we be clear?"
The 70-year-old said it had been Ms Lawson's idea to give the sisters credit cards and that they did most of the family's personal shopping as part of their roles as assistants.
He told the jury that when he saw the amounts being spent he thought the Grillo sisters had been "naughty" and had wanted to put the matter behind them whereas Ms Lawson wanted to call the police.
Earlier the jury heard from the couple's accountant Rahul Gajjar who said he had increased the sisters' credit limit to £100,000 without telling the art dealer.
Mr Gajjar, 44, said there was "lax control" of spending on cards issued to staff.
Mr Saatchi told the court: "I've very bad at finances. I don't take any interest at all."
Mr Saatchi said the "slavery story" - the defendants complained they were "being treated worse than Filipino slaves" - was "nonsense".
He said Miss Lawson was a "very, very nice employer", adding: "The staff all adored her."
He denied that Ms Lawson would have told her staff to spend whatever they wanted.