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The former prime minister was reportedly present in March last year when Murdoch's two daughters by his third wife were baptised on the banks of the Jordan.

The information was not made public and its disclosure in an interview with Mrs Murdoch in Vogue will prove highly embarrassing for Mr Blair.

His close ties to the Murdochs could explain his reluctance to condemn the News International phone hacking scandal.

In July, it was reported that he asked Gordon Brown to put pressure on Tom Watson, the Labour MP who helped expose the scandal, to drop his investigation.

Mr Blair's spokesman categorically denied the allegation.

When the baptism was splashed across the pages of Hello! magazine last year, Nicole Kidman and Hugh Jackman, her fellow Australian actor, were named as godparents to Grace, nine, and Chloe, eight.

No mention was made of Mr Blair's role as a godfather to Grace and he did not appear in pictures of the ceremony, which took place at the spot where it is said that Jesus was baptised.

However, the facts emerged in an interview with Mrs Murdoch in the fashion magazine.

She made international headlines in July by jumping to the defence of her 80-year-old husband when he was attacked with a "foam pie" while giving evidence to a parliamentary committee on hacking.

Last night, Mr Blair's spokesman refused to comment, but a News Corp source confirmed that Mr Blair was godfather to Grace, as was Lachlan Murdoch, Rupert Murdoch's eldest son.

The journalist who conducted the interview for Vogue is said to move in the same circles as the Murdochs in New York.

While Mrs Murdoch does not comment on Mr Blair directly, the article states that Miss Kidman, Mr Jackman and Mr Blair are godparents.

It claims that Mr Blair attended the Jordanian ceremony "garbed in white" and describes him as one of Mrs Murdoch's "closest friends".

They have a mutual friend in Queen Rania of Jordan, who hosted the baptism. Both women were recently on the judging panel for a film prize organised by the Tony Blair Faith Foundation.

Mrs Murdoch, 42, rarely gives interviews but spoke to Vogue to publicise a new film, Snow Flower and the Secret Fan, which she has produced.

Speaking on the eve of her 80-year-old husband's appearance before the Commons select committee, she said of the phone hacking scandal: "Of course, as Rupert's wife, I think it's unfair on him to be going through this.

"I worry about him being alone. He has no PR people advising him. He tells me not to come but I'm flying to London for the hearing. I want to be with him."

Mrs Murdoch said she had not slept for weeks due to stress.

Days later, she made headlines around the world when she leapt up to defend her husband against a protester wielding a foam pie.

Mrs Murdoch also discussed her poverty-stricken upbringing in China - a far cry from the billionaire lifestyle she now enjoys. "I grew up in a little funny town called Xuzhou, in the countryside, very poor," she said. "I had never even been in a supermarket before coming to America."

Her family did not own a fridge until she was 15 and "my parents wouldn't let me open the refrigerator door because they worried I would damage the door by opening it too many times".

Her engineer parents insisted that she study medicine, but she dropped out of her course. She was befriended by an American woman, Joyce Cherry, who taught her English and offered to sponsor her to study at California State University.

Having taken up the offer and moved in with the family, she embarked upon an affair with Mrs Cherry's husband, Jake. He divorced his wife and married Wendi. The marriage lasted four months, during which time she gained a Green Card.

She gained an MBA from Yale Business School and progressed to Murdoch's Star TV network in Hong Kong, where she met her future husband.

Describing their first encounter in 1998, she said: "Rupert was in a meeting and he was asking what was going on in China. They brought me into the meeting and that was how we met."

They married in 1999 on Murdoch's yacht. The wedding took place 17 days after Murdoch's divorce from Anna, his wife of 31 years and mother to Lachlan, James and Elisabeth.

Nicole Kidman told the magazine that she and Mrs Murdoch are kindred spirits.

"Wendi is all about friendship between women," she said. "We just clicked. I was brought up in the Church and believe that it is important to have a moral compass, wherever you find it. Wendi also has found it through Church and Sunday school."

The full interview is in the October issue of Vogue, out on Thursday.