Helena Bonham Carter once had a sleepover at Windsor Castle

She said: "It's fun! Rachel Weisz was there with James Bond. I stayed in Prince Charles's rooms. We had supper and the Queen and Prince Philip gave us a tour."

The visit was made even more special by the fact each guest was given something from the royal archive that had a connection to them, with 'Alice in Wonderland' director Tim presented with a first edition of Lewis Carroll's classic fairytale and Helena - who portrayed the Queen Mother in 'The King's Speech' - given a letter from King George VI's speech therapist.

She added in an interview with Radio Times magazine: "They'd found something from their archive that each of us would appreciate.

"So Tim had the first edition of 'Alice in Wonderland', I had a letter from Lionel Logue, who was the King's speech therapist.

"It was really touching."

The 53-year-old star plays the queen's late sister, Princess Margaret, in the new series of 'The Crown' and has previously admitted she spoke to the royal - who died in 2002 - via a medium before taking on the role.

And Helena has also admitted the spirit told her to perfect her smoking technique.

She said: "I asked her via a medium! Oh, she has a great sense of humour.

"She reminded me to be neat and get my smoking right. It's true -- I'm barking!"