The Duke and Duchess of Cambridge got married in 2011 at Westminster Abbey, in a service that was viewed by billions across the globe.
During the historic ceremony, Harry called their romance an “inspiration”, MirrorOnline reports.
Royal author Katie Nicholl gave details of Harry’s speech in her 2017 biography “Harry: Life, Loss, and Love”.
She wrote: “It was affectionate, warm and funny and touched William deeply.”
It affected Harry’s girlfriend at the time, Chelsy Davy, along with Kate.
She continued: “When he said the couple’s decade-long romance was his inspiration, there was a shy smile from Chelsy, while Kate shed a tear.”
Ms Nicholl continued: “The speech was peppered with Harry’s classic sense of humour, and he ribbed his brother: ‘William didn’t have a romantic bone in his body before he met Kate, so I knew it was serious when William suddenly started cooing down the phone at Kate.’
“Famous for his mimicry, Harry then impersonated his brother calling Kate ‘Babykins’, to much laughter from the guests.”
Harry’s girlfriend supposedly made him delete one line before giving the speech.
Ms Nicholla added: “She had helped Harry edit the best man’s speech, sensitively advising him to take out a line about Kate’s ‘killer legs’ that might have embarrassed the bride.”
Earlier this month, a royal expert warned the pair’s relationship could be beyond repair following the publication of biography Finding Freedom.
The royal brothers’ widely publicised “feud” was one of the book’s central themes.
Harry himself admitted a break-down in his relationship with the Duke of Cambridge in an ITV documentary last year.
But, according to Vanity Fair’s royal correspondent Katie Nicholl, the duo were starting to mend bridges in the build-up to the book’s release.
In a clip Daily Star Online has obtained from upcoming Channel 5 documentary Meghan & Harry: The New Revelations, she said: “The irony about this book, in many ways, is that the brothers were just getting to a stage in their relationship where they were on a more even keel.
“I was told that communication had resumed between the brothers.
“We don’t know whether they’ve spoken in light of the excerpts from this book.
“But one can only imagine this has done nothing to improve relations that were strained in the beginning and at this stage must seem pretty beyond repair.”