The Queen "flushed scarlet" when Prince Philip complimented her dress in an intimate moment behind closed doors.
The furiously private couple, who were married for 73 years, would remain professional in public settings or during royal engagements, so it was rare to see any sort of affection.
But a royal insider has shared an insight into what went on behind the scenes.
Designer Ian Thomas, who worked with the Queen for more than 20 years, recalled the moment that Prince Philip made Her Majesty blush.
Speaking on Channel 5's Secrets of Royal Dressmakers, royal expert Ingrid Seward shared the sweet story which took place while Thomas adjusted the hem of his latest creation.
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Ingrid says: " When he was doing the hem, Prince Philip walked through the Queen’s dressing room and said ‘hmh, nice dress.'.
"The Queen flushed scarlet. I always remember him telling me that story. She was just so thrilled to get the compliment from her husband."
Mr Thomas, who owned his own couture business in Belgravia, London, made many outfits for the Queen and for other royal women too.
In 1973 he was awarded a Royal Warrant as dressmaker for his work.
The Queen is always perfectly dressed and her use of block colours and pretty pattern has worked for decades.
But the same couldn't be said for all the royals, as during the programme, one of the experts described Sarah Ferguson as the "worst dresser of all time."
Ingrid said: “The worst dresser of all time was definitely Fergie.
"She looked great in her own clothes, in jeans and t-shirts but she was just a disaster in the fashion of the 80s because it was just too much for her.
"It was too frilly, there were too many bows. She said so herself.”
However, as she's got older, Fergie learnt what suits her, and what doesn't Emily Andrews said.
She said: "As an older woman now she has got her style absolutely on point.
"She’s got really good legs, she always wears dresses or pleated skirts, a top and a blazer and she’s got that lovely red hair."
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