Earl Spencer has revealed how he repeatedly rehearsed the eulogy to his sister, Princess Diana, and even read it to her coffin in St James's Palace.
The Earl found delivering his sister's eulogy a terrible ordeal
In an article in The Guardian, he said that in response he "heard a whisper that sounded like satisfaction".
He said he was proud that "every word I said was for Diana... and was true".
His promise at the funeral in 1997 that Princes William and Harry would be protected by "blood family" was seen as an attack on the Royal family.
The Earl has said in previous interviews that he had no other agenda than to deliver a eulogy from the heart.
He has written an account of how he wrote the controversial address as part of a Guardian series on rhetoric.
The Earl describes how he struggled with what to say but was galvanised into action early one morning when he realised that he would be speaking for Diana's supporters as well as for her family.
The two themes he had found most common in all the letters he had received were concern that William and Harry would be "led away to an unhappy upbringing" and "revulsion at the gutter press".
He finished the oration in two hours in a stream of writing "that came more from my heart than from my head".
'Faint and weak'
"I had practised the speech to myself repeatedly over the days preceding the funeral, trying to familiarise myself with the passages that might lead me to break down, a very real possibility.
"I read it to Diana's coffin, in the chapel at St James's Palace, and at the conclusion heard a whisper that sounded like satisfaction in that sad, sad, place," the Earl writes.
Despite his practice, he said delivering the words was a "terrible ordeal" that left him "emotionally in tatters".
The Earl said he felt "faint and weak" as he gave the eulogy
The Earl reveals how he felt "faint and weak" as he began to speak and "never heard" the applause as he finished.
In the weeks after the funeral he received more than 100,000 letters from all over the world, which he attempted to answer.
He says that he wishes his sister's funeral were still "decades in the future".