A man walks past an eel, pie and mash shop displaying a flag depicting Britain's Prince William and Kate Middleton and a poster of Princess Diana, in north London April 26, 2011. Prince William and Kate Middleton will marry at Wesminster Abbey on April 29th. [Photo/Agencies]

LONDON - Elton John was last at Westminster Abbey 14 years ago when he sang the haunting "Candle in the Wind" at the funeral of his friend Princess Diana.

On Friday, the British singer will be back as a guest at the wedding of her elder son Prince William, a happier occasion at which his mother's absence will nonetheless be keenly felt.

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More than one million people lined the route of Diana's cortege in 1997 to pay their respects to a woman who was a royal outcast by the time of her death aged 36 in a Paris car crash but a hugely popular figure with the public.

For many, the abiding memory of William is still as a 15-year-old boy, head bowed, following his mother's coffin through the packed streets of London watched by hundreds of millions more people around the world.

"The last time we were in Westminster Abbey, my heart sank when I saw those two boys walking behind the coffin," Elton said, referring to William and his younger brother Harry.

"I can't imagine at that young age having to walk in public following your mother's coffin," he added in an interview with US television host Barbara Walters.

"And the next time we are in the Abbey it's to see him walking up the aisle with a beautiful woman and the love of his life," said Elton, who was knighted by Queen Elizabeth for services to music and charity, adding:

"I think it's the most joyous result and I'm sure Diana would be very, very happy about it."

Media executives say the "Diana connection" is one reason why the public appetite for coverage of the wedding, particularly in the United States where she had an army of admirers, is so strong.

Elton John's "Candle in the Wind 1997" became the best-selling single worldwide since charts began with 33 million copies sold.