Pippa and James Middleton expressed their feelings openly when Kate revealed that she and Prince William were getting married.
According to James Middleton's new book, the Princess of Wales’s younger siblings were informed of the news at a local pub. James mentioned that he and Pippa assured Kate of their unwavering support.
He wrote: "We make a quiet acknowledgement that we’ll always be there for each other, look out for one another, support each other.
"No matter how crazy things get."
He added in a separate passage: "Catherine rings to let me know" ahead of the announcement being made public later that day.
The 37-year-old also shared in his memoir, Meet Ella: The Dog Who Saved My Life, that he was taken aback when his sister and future brother-in-law asked him to do a reading during their 2011 wedding at Westminster Abbey.
"A reading? I thought they were joking," he wrote.
"My mind raced back to school and my stumbling, incoherent efforts to read in front of the class.
"What were they thinking? Being dyslexic, reading is my least favourite occupation."
He recalled asking them: "Seriously?" Kate and William responded: "Seriously."
Kate's brother admitted: "If that was what my sister and William wanted, then of course I’d do my best not to let them down."
James's reading was the only Bible reading in the service, and he wrote he did not know "whether to be honoured or appalled" at the time.
He then practised for months in order to recite it properly.
"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," he explained.
"I wanted to do [Kate and William] both proud,” he said. “I glanced up and saw happy faces I recognised in the congregation and the nervousness fell away. I took a deep breath ... and began."
After the nuptials, he revealed he "received thousands of messages and invitations to read lessons at churches around the globe".