Prince George and Princess Charlotte were spotted laughing at the Queen's admission that she keeps an emergency stash of marmalade sandwiches in her handbag.
The royal siblings were clearly delighted at the revelation, which the Monarch made during a surprise comic appearance with Paddington Bear.
The monarch and the famous bear met for a chaotic cream tea at Buckingham Palace in a special, secretly-pre-recorded sequence played at the start of the televised BBC's Platinum Party at the Palace.
The duffle-coat wearing bear told the Queen how he ensured he always had his favourite treat on him just in case, lifting up his red hat to reveal his snack.
The Queen responded by saying: "So do I," before opening her bag and declaring: "I keep mine in here", before showing her very own ready-made supply of the bread and orange preserve staple, adding: "For later."
Paddington caused raised eyebrows from a Palace footman by gulping down his tea from the spout of the teapot, and leaving none left for the amused Queen, who declared: "Never mind."
The accident-prone bear was shown causing mayhem by accidentally spraying a splodge of cream from a chocolate eclair onto the footman's face.
The bear, from deepest darkest Peru, congratulated the Queen on her reign of 70 years, saying: "Happy Jubilee Ma'am. And thank you. For everything."
The modest Queen replied: "That's very kind."
The unlikely duo then tapped out the beat of the We Will Rock You anthem together on china teacups using silver spoons as a unique way of getting the concert under way.
With the two-and-a-half-minute film played at the start of the televised BBC's Platinum Party at the Palace, the novel duet tapped out the rhythm for opening act Queen + Adam Lambert - who joined in on the main stage.
It brought back memories of the Queen's James Bond skit for the London 2012 Olympic opening ceremony, when the monarch met 007, played by Daniel Craig, and then appeared to parachute into the stadium, with the help of a body double.
Paddington and the Queen were pictured sat opposite each other in ornate chairs at a table, laid for afternoon tea, covered with a white linen cloth in an opulent room.
Buckingham Palace said the Queen felt the opportunity to invite Paddington to tea was "too fun to miss".
The Palace said: "Her Majesty is well known for her sense of humour, so it should be no surprise that she decided to take part in tonight's sketch.
"There was an interest in the filming and animation process and the opportunity to invite a famous bear to tea was just too much fun to miss.
"While The Queen may not be attending the concert in person, she was very keen that people understood how much it meant to her and that all those watching had a great time."
The film was kept under wraps for several months by Buckingham Palace, BBC Studios and Heyday Films/StudioCanal. Actor Ben Whishaw voiced Paddington, just as he did in the hit movie versions of the children's story.
Those involved in the film, which was actually shot at Windsor Castle, praised the Queen's wit and warmth during the process, saying she shone and put them all at ease. Rosie Alison of Heyday Films said:
"Filming Her Majesty's tea party with Paddington Bear was such an emotional day for the entire crew.
"All of us were in awe of the Queen's wit, warmth and radiant aura as she patiently engaged with a polite, clumsy but very well-intentioned bear.
"Of course, she shone, and put Paddington (and all of us) at ease. Capturing this lovely encounter was an absolute joy and unique privilege for the whole team."
Paddington, created by late British author Michael Bond, and the Queen share something in common - they both have two birthdays.
When Paddington was adopted by the Brown family, they agreed that bears, "just like the Queen", have two birthdays every year.
The Queen's actual birthday is on April 21, but she has an official one each year in June. Paddington's birthdays are on June 25 and December 25.
He has visited the Queen before - with a costumed Paddington going to Buckingham Palace in 2006 for a children's party filled with storybook characters as part of the monarch's 80th birthday celebrations.
