The director and the music icon first met in 1993, got a civil partnership in December 2005 and in 2014, when same-sex marriage became legal in England and Wales, officially tied the knot.

Speaking at the gala event for the new documentary Elton John: Never Too Late, the actor and producer says the 77-year-old Rocketman singer has changed in a beautiful way since they first got together.

"He's so much more comfortable with himself. He's so much more happy. He's so much more grounded," the 61-year-old tells Sky News.

"Elton is very proud of what he's achieved professionally but he's most proud of our family and the great joy in his life comes from raising our sons and they're very special - we couldn't love them more than we do.

"And it's just an entire new journey of discovery that we're going on together. And I feel really blessed at this stage in my life to have that opportunity."

Furnish has teamed up with Emmy award-winning filmmaker RJ Cutler to direct the documentary that follows the superstar's life and love for music.

The project includes never-before-seen footage and conversations with the artist's long-time songwriting partner Bernie Taupin, as well as Dua Lipa and the late John Lennon.

Furnish adds: "A friend of mine had an expression [about Sir Elton] - 'a major participant in life'. I think that really sums him up because he's just so connected to our world and always looking forward."

This isn't the first time the couple have worked together on a project - Furnish is the CEO of Rocket Entertainment, the chair of the Elton John AIDS Foundation, and also worked as his husband's manager.

He says the decision to finish his career as a performer last year was Sir Elton's as he wanted to make sure he went out "on a high" performing and singing "at his best".

Furnish says: "Elton doesn't do anything by halves. He is a complete force of nature."

The documentary film was shown at a special gala screening at the Royal Festival Hall as part of the London Film Festival.

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Cutler says it deals with the theme of mortality and seeing Sir Elton find his way to his "truest self" with his husband and their children Zachary and Elijah.

He says: "People with children will tell you that it's almost hard to remember what life was like before they arrived, and you actually believe that."

Cutler adds: "Even with someone like Elton John, who had such a rich life, but on some important level, as he said 'I don't want my gravestone to say he sold a million albums, I want my gravestone to say he was a great dad and a great father and a great, husband.'

"This is a movie about mortality and about the fact that we're all here for a brief moment and even Elton John recognises that. His openness to exploring that and his connection to his family and exploring that was all very moving to me."

Elton John: Never Too Late premieres on 13 December on Disney Plus.