Landmark royal documentary narrated by Helena Bonham Carter takes behind the scenes look at King Charles’s first year as monarch… including the moment before his Coronation when he donned his ermine gown and joked ‘I can fly!’

It's a moment of wide-eyed, almost childlike excitement in the making of history.

King Charles, just before leaving Buckingham Palace for his coronation in May, waves his velvet and ermine state robes and laughs: “I can fly!”

The candid moment is captured in a groundbreaking new 90-minute documentary narrated by Helena Bonham Carter, offering an exclusive behind-the-scenes look at his first year as monarch.

Charles III: The Coronation Year, which airs on Boxing Day, is a highlight of the BBC's Christmas programme.

It is the first time a crew has been given fly-on-the-wall access to the Royal Family ahead of such a momentous national event.

It was written and co-produced for Oxford Films by The Mail's royal expert Robert Hardman, who provides more wonderful details in today's Weekend Magazine.

The program includes interviews with family members, especially Princess Anne, and staff responsible for making the King's big day a success.

On Saturday morning, May 6, King Charles and Queen Camilla are involved in the last-minute preparations at Buckingham Palace.

Down the hall Her Majesty walks out in her Bruce Oldfield embroidered ivory dress, accompanied by her pages – whom she affectionately calls 'the boys'.

“Very slowly, together,” she says. Lady Lansdowne, one of Camilla's two official ladies present that day, says of the moment: 'It wasn't until we were all ready that we actually all came together to see each other for the first time.

'She hadn't seen our dresses and we hadn't seen her dress. That was a very special moment. It looked a bit like a wedding. It was the bridesmaids who went to visit the bride.'

The images show the queen walking gingerly towards the exit, accompanied by her three grandsons and great-nephew.

“Don't step on my dress or there will be a problem,” Camilla reminds them fondly.

She adds, smiling to the cameraman, “Here we are, with all the boys.”

The King then appears in conversation with his equerry Lieutenant Colonel Johnny Thompson, smiling and helping to ease everyone's nervousness by waving the mantle of state that his grandfather, King George VI, wore at his coronation in 1937, during his own 'I Can Fly Titanic moment. .

Camilla also jokes, “Someone's always getting pulled over,” referring to the weight of their finery.

As the couple depart for Westminster Abbey in the Diamond Jubilee State Coach, Lady Lansdowne, lifelong friend of the Queen, comments: 'It was a very exciting moment to get them into that carriage for the first time and then we set off.'

In an exceptionally moving clip, Camilla's other lady present, her sister Annabel Elliot, waves her goodbye and dabs her face with a handkerchief, apparently moved to tears.

She recalls: 'I thought back to when I was two years old and watching the Queen's (Elizabeth) coronation on a little black and white television – and there goes this golden carriage with my sister in it.

'It's so surreal and this can't be happening. Yes, it was quite a moment.' Lady Lansdowne added: 'We were ready to go out and literally face the world.'

Other charming images show a rehearsal in the abbey. Charles and Prince William practice with the Archbishop of Canterbury, Justin Welby.

The Archbishop later says on camera that his memory is worse than that of his family dog ​​and that his words are mixed up, much to the king's amusement.

He says: 'I have a memory that is probably about as good as our spaniel's – in other words, zero.'

He rattles off what should be a familiar blessing: “And the blessing of God Almighty, the Father, the Son, and the Holy Spirit, be among you and abide with you now and… no, that cannot be true?”

The Archbishop of York 'and always' helpfully intervenes, jokingly adding: 'I'm sure you've said this before?' Everyone – including the king – is helpless with laughter.

“You knew that was coming,” the monarch chuckles.

Welby continues, “Be with you and stay with you always.” Still smiling and shaking his head, Charles adds, “Amen. Beautiful.'

Princess Anne emphasizes her brother's sense of duty.

'Monarchy is a 365 day a year business. And it doesn't stop because you change monarchs for whatever reason,” she says.

Charles III: The Coronation Year airs on Boxing Day at 6.50pm on BBC One.