Touched by the efforts they are making to help celebrate her big day, Elizabeth smiles as she turns away from the window. She keeps smiling as she stands patiently for an hour or more while the Hartnell team start the long process of dressing her, checking that every stitch and seam sits perfectly.

They melt away when Monsieur Henri arrives to do her hair, only to reappear to fit the veil, but disaster strikes when her grandmother’s diamond tiara snaps in two as they adjust it on her head.

The crack splinters the buzz of excitement in the room and is followed by an appalled silence. For the first time, Elizabeth’s smile falters.

‘It just came apart in my hands …’ The assistant in charge of the tiara lowering is white-faced and near to tears.

‘Can you fix it?’ Elizabeth asks.

The assistant just looks at the two pieces of the tiara in her hands.

‘Mummy …’ Elizabeth looks helplessly at her mother who steps forward and attempts to calm everyone down.

‘There’s no need to upset yourself, Lilibet. One thing we’re not short of here is tiaras. I’ll ask my dresser to find another. Remember the one Mr Hartnell suggested originally?’

‘No, I want this one. Granny lent it to me for the wedding.’ It’s not like Elizabeth to be fretful but all at once, it seems impossible to be married without Queen Mary’s tiara.

The thought of her grandmother, the Big Potato as Philip calls her now, brings ridiculous tears to her eyes.

The Queen exchanges a look with Bobo. ‘Call the court jeweller,’ she says quietly. ‘Get him here straight away.’

Smiling, she turns back to Elizabeth. ‘There’s plenty of time – two hours until you’re due to leave for the Abbey.

‘Yes, of course.’ Elizabeth takes a deep breath and makes herself calm down.

‘You look like a fairy-tale princess,’ her mother tells her.

She really does, Elizabeth thinks. The dress is as beautiful as Mr Hartnell promised. It shimmers with seed pearls and tiny crystals that catch the light. ‘It needs the pearl necklace.’

‘This one?’ Still in calming mode, the Queen picks up Elizabeth’s favourite strand of pearls from the dressing table. They’re the ones she usually wears, but it’s not the necklace she has in mind for the wedding.

‘No, the double strand you and Papa gave me. Bobo, where is it?’

Bobo and the Queen exchange another look. ‘It’s still on display in St James’s Palace,’ Bobo says carefully.

‘Someone can go and get it.’ Elizabeth has made up her mind. ‘Ask Jock Colville to come in.’

Her private secretary is summoned but looks dismayed when Elizabeth asks him to fetch the necklace.

‘From St James’s Palace?’ he repeats cautiously.

‘It’s not that far.’

He hesitates. ‘Not usually, no, but there must be a hundred thousand people crammed between here and there this morning.’

‘Please, Jock.’

‘Certainly, Your Royal Highness.’ Clearly daunted, Jock withdraws with dignity but the moment the door is shut behind him, they can hear him charging off down the corridor at speed.