The 'Tiny Dancer' singer was one of a handful of celebrity guests invited into Westminster Abbey in London to see the royal couple wed, and as he watched the union, he appeared almost moved to tears.
Elton was sat next to his husband, David Furnish, in The Front row of the Abbey for the proceedings. The singer was a close friend of William's mother Diana, and performed at her funeral after her death in a car crash in 1997.
Other celebrities among the wedding's 1,900 guests included soccer star David Beckham and his wife Victoria, invited after David worked closely with the prince on England's bid to host the 2018 World Cup.
The couple described the ceremony as "beautiful and heartfelt," before adding to BBC news: "Catherine looked wonderfully elegant, and we were honoured to be part of such a special, historical day for our country.
"We wish Catherine and William much love and happiness for the future."
Many celebrities took to twitter to pay their respects to the happy couple, including singer George Michael, who had recorded a version of Stevie Wonder's track 'You and I' as a present for the couple.
During the wedding service he tweeted: "One word... Class (sic)."
'California Gurls' singer Katy Perry decided to pay her own tribute by decorating her nails with different pictures of William and Kate.
She posted the picture with an accompanying tweet reading: "In honor of the Royal Wedding, I present you... My royal NAILS! CONGRATS (sic)."
In July of 2015, Ed Sheeran played his biggest gigs to date, selling out Wembley...
It's fair to say that Vincent Furnier made musical history when he became Alice Cooper;...
Elton John is one of the biggest and most glamorous rockstars of all time having...