James Middleton has described his candid seven-word reaction to a request from his sister Princess Kate ahead of her wedding to Prince William.

The 37-year-old was asked to perform a Bible reading at Princess Kate’s marriage in Westminster Abbey in 2011.

In his forthcoming memoir Mr Middleton, who was diagnosed with dyslexia at 11-years-old, admits he was taken aback by the request.

His reaction, he recalled, was: “A reading? I thought they were joking.”

In an excerpt from the book, entitled Meet Ella: The Dog Who Saved My Life and published by the Daily Mail this weekend, he added that reading is his “least favourite occupation”.

He said he had “fibbed breezily” and said he would do it, noting that he hoped not to let William and Kate down if that was something they wanted – but noted that he was not sure whether to feel “honoured or appalled”.

Mr Middleton said he had ended up taking a copy of the speech with him everywhere he went “for months” in the build-up to the wedding.

He added: “I ­carried it with me everywhere, taking it out of my pocket to practice the lines, over which I tripped and stumbled, transposing syllables, getting my ps and bs — my nemeses — in a twist.”

Mr Middleton also received training from noted voice coach Anthony Gordon Lennox, who had previously helped Prime Minister David Cameron.

He added Ella, the pet dog his memoir is named after, was there during his practices – but was not allowed into Westminster Abbey for the wedding itself.

On the day of the nuptials, in April 2011, Mr Middleton recalled taking a “crumpled phonetic copy” of his reading into the abbey for the ceremony – saying that he wanted to make the royal couple proud.

He recalled: “I glanced up and saw happy faces I recognised in the congregation and the nervousness fell away. I took a deep breath … and began.”

While the event was watched by hundreds of millions of people around the planet, Mr Middleton celebrated in a more subdued fashion.

He said: “After all the wonder of the day, the service, then the celebrations, all I wanted to do was throw on a pair of old jeans and take Ella out for a walk.

“It wasn’t until then that I allowed myself to think about how momentous the day had been.”