British pop superstar Elton John has married long-time partner David Furnish on the ninth anniversary of their civil partnership.
The 67-year-old singer posted a picture on social media of himself and Furnish in blue suits signing a form.
"That's the legal bit done. Now on to the ceremony!" said the caption.
Football superstar David Beckham, comedian David Walliams and actor Hugh Grant were among the guests to arrive through the gates of the couple's estate in Windsor, west of London, close to the castle where Queen Elizabeth II spends much of her time.
Around 50 guests, also including singer Ed Sheeran, Elizabeth Hurley and Ozzy and Sharon Osbourne, have reportedly been invited to the ceremony.
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The musician had earlier posted a picture of an invitation on his Instagram page, with the words "Sir Elton John and David Furnish request the pleasure of your company to celebrate their wedding on Sunday the 21st December" written on a background of red roses.
While known for his flamboyance, the ceremony is expected to be "a small, intimate do" with guests being served festive canapes and mulled wine.
It is believed the ring bearers will be the couple's two sons, Zachary, three, and Elijah, 23 months.
The singer voiced pride that England and Wales began allowing same-sex marriage in March. Scotland followed suit this week.
John and Furnish - who divide their time between England, Beverly Hills, Atlanta, Venice and Nice in the south of France - entered a civil partnership soon after the institution began in Britain in 2005 and have now been together for 21 years.
The 2005 celebration was a much grander affair, with 650 guests invited.
"Sir Elton", who was knighted in 1998, was ranked number four in the most recent Sunday Times newspaper Rich List of British and Irish musicians, with a personal wealth estimated at $438 million.
Early in his career, John hid his sexuality and married a woman. But he later became an advocate for gay rights and has been active in the fight against AIDS.
