The queen appeared in a sketch before the festivities got underway.
Queen Elizabeth sure knows how to get the party started. Her Majesty was joined by the lovable Paddington Bear character in a sketch to kick off the star-studded Platinum Party at the Palace."
In one of the videos, Elizabeth is sitting across Paddington as they are about to embark on an afternoon tea. Paddington looks up and says, "Thank you for having me. I do hope you're having a lovely Jubilee." The queen then asks Paddington if he wants tea and he says, "Oh, yes, please" before he throws all manners -- and royal etiquette, for that matter -- out the window when he gets up on his chair and starts chugging the pot of tea. It's a hilarious sketch from start to finish.
And, speaking of finish, another video shows the sketch end with Elizabeth and Paddington rocking out to the Queen classic, "We Will Rock You," which drew a boisterous ovation from the packed crowd watching from The Mall.
A spokesperson for the Palace tells ET that the sketch was shot in March.
"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," the spokesperson added. "There was an interest in the filming and animation process and the opportunity to invite a famous bear to tea was just too much to miss."
Prince William and Kate Middleton had front-row seats and they were joined by two of their three children -- Prince George and Princess Charlotte -- who sat between them and soaked up the festivities. Prince Charles and Camila, Duchess of Cornwall also got a front-row view. A source close to the Palace tells ET that other attendees include Earl and Countess of Wessex and their children; Princess Royal & Sir Tim; Princess Beatrice & Edoardo Mapelli Mozzi; Princess Eugenia and Jack Brooksbank; Peter Phillips and children and Zara and Mike Tindall.
Prince Harry and Meghan Markle are not scheduled to attend, as they're celebrating their daughter Lilibet's first birthday. The Queen herself is not attending the night's festivities but she is said to be watching it from the comfort of Windsor Castle.
The evening will feature a three-stage "Platinum Party at the Palace," streaming on BBC, hosted at Buckingham Palace. Diana Ross, Queen and Adam Lambert, Alicia Keys, Duran Duran, Hans Zimmer, Ella Eyre, Craig David, Mabel, Elbow, George Ezra, Andrea Bocelli, Mimi Webb, Sam Ryder, Jax Jones, Celeste, Nile Rodgers, Sigala and Diversity are all set to make appearances.
The night doesn't stop there! Sir David Attenborough, Emma Raducanu, David Beckham, Stephen Fry, Dame Julie Andrews, and The Royal Ballet will also attend, and Sir Elton John submitted a specially recorded performance.
Finally, Andrew Lloyd Webber and Lin-Manuel Miranda will make a joint appearance, along with performances featuring guests from The Phantom of the Opera, Hamilton, Six, The Lion King and Joseph and the Amazing Technicolor Dreamcoat.