It may be Charles's big day but one of his coronation guests has stolen the show at Westminster Abbey.
Royal fans couldn't help but get a little distracted from watching Charles be crowned king when they spotted the coolest-looking guy in the crowd.
Sitting beside musical theatre composer Andrew Lloyd Webber was a man with an impressively large handlebar moustache, a head of long grey hair, and a pair of tinted sunglasses.
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While his time-travelling Beatle look stood out a little amongst the coronation robes, suits, and gowns, he definitely made an impression on viewers watching the service at home.
As soon as his face appeared on-screen, people took to Twitter in a desperate effort to try and figure out who this cool guy was, and how he ended up in Westminster today.
"Who is the guy with the handlebar moustache near Lloyd Webber? #Coronation," one user asked the people of Twitter.
"Precisely what I want to know," replied a second.
Sharing a photo of him on her television screen, another tweeted: "Well I’m all agog! Who on earth is that next to Mr Lloyd-Webber, surely it’s someone in a disguise…"
Thankfully, some people recognised this coronation attendee, and were happy to bring the desperate search to an end.
The owner of that handlebar moustache is none other than Sir Karl Jenkins - a composer and multi-instrumentalist who composed a piece for today's coronation.
Sir Karl Jenkins, 79, composed a piece called 'Tros y Garreg', which translates to 'Crossing the Stone'.
The piece, which Jenkins describes as 'haunting' and 'very Welsh', was performed on Saturday by the coronation orchestra and royal harpist Alis Huws
It's part of a concerto that was commissioned by King Charles III over two decades ago, back when he was the Prince of Wales.
The inclusion of Welsh music in the coronation is said to reflect King Charles's support of Welsh culture.
Speaking ahead of the ceremony, Sir Karl told the BBC: "I am very honoured. It obviously sums up Welsh culture - the harp - and he [the King] has always supported Welsh music.
"I don't know whether he chose it, but he was happy to have it there. I know he likes it otherwise he wouldn't have asked me."
The composer also spoke about his memories of Queen Elizabeth II's coronation in 1953, which he watched when he was just eight years old from Swansea.
"We had one of the first TV screens in the street, in the village I guess...12in (30cm) screen, two rows of friends and neighbours watching," he recalled.
Now, some seventy years later, he's got a much bigger part to play.
Speaking on the transition from one coronation to another, he simply said: "It's quite a jump isn't it?"
Topics: King Charles III, Royal Family, UK News, Twitter
Ali Condon