Dame Helen Mirren has been named best actress at the Academy Awards for her performance in The Queen.
"All kids love to get gold stars, and this is the biggest and the best gold star that I have ever had," she said.
A Buckingham Palace spokeswoman said she was "sure that the Queen will be pleased" by Dame Helen's victory.
Martin Scorsese's crime drama The Departed won four awards, including best picture, while the film-maker won his first Oscar for best director.
Alan Arkin won best supporting actor for Little Miss Sunshine, which also picked up best original screenplay.
Jennifer Hudson was named best supporting actress for her first film role, in the musical Dreamgirls.
The adapted screenplay prize went to the script for The Departed, which also won for editing.
The best actor Oscar went to Forest Whitaker, who had been favourite to triumph for his performance as the Ugandan dictator Idi Amin in The Last King of Scotland.
Dame Helen had also been overwhelming favourite to add the best actress Oscar to a substantial awards haul that has included a Bafta, Golden Globe and Screen Actors Guild prize.
She plays Elizabeth II in the British movie about the Royal Family's reaction to the 1997 death of Princess Diana.
Bookmaker William Hill started paying out last week on bets on her victory, with other firms agreeing she was the strongest ever Oscars favourite.
Academy Awards host Ellen DeGeneres had joked to the audience early in the ceremony: "It's exciting because you don't know who's going to win - unless you're British, and then you know you've a pretty good shot."
Accepting her award, Dame Helen said: "For 50 years and more, Elizabeth Windsor has maintained her dignity, her sense of duty and her hairstyle.
"If it wasn't for her, I most certainly wouldn't be here - ladies and gentlemen, I give you the Queen."
Speaking to BBC Breakfast after the ceremony, she added: "I had to recognise the person that I was playing and everything that she means to us and to me and to the history of our country and all the rest of it."
Dame Helen will now meet the real monarch for lunch, it has emerged.
The Queen has invited Dame Helen, director Stephen Frears and screenwriter Peter Morgan to Buckingham Palace, Morgan said.
"We have been invited to meet her," he said. "The Queen's private secretary has invited us for lunch - Stephen, Helen and myself."
But Dame Helen said she did not expect a congratulatory telephone call.
"I'm not expecting a call from Her Majesty, not ever," she said. "I think it's wonderful that I live in a country that allows us to make a film like this."
Tony Blair, whose spokesman said he had not seen The Queen, welcomed Dame Helen's Oscar win.
He said: "It takes a very special kind of actress to take on a role of this kind and to do so to universal acclaim. Helen Mirren is a very special kind of actress and her Oscar is well deserved."
Mr Blair is portrayed by Michael Sheen in the movie.
UK broadcaster ITV, which partly financed the film, has sent the actress its congratulations.
"We're delighted Helen's fantastic performance was rewarded with a well-deserved Oscar and look forward to the film being shown on ITV in the autumn," a spokeswoman said.
Scorsese had previously been nominated as best director but lost out on five occasions, for classic movies including Raging Bull and Goodfellas.
"Could you double-check the envelope?" he joked as he collected his award.
He went on: "So many people over the years have been wishing this for me - strangers. I walk in the street and people say something to me: 'You should win, you should win.'"
The best animated feature film Oscar was awarded to Happy Feet, while Germany's Das Leben der Anderen (The Lives of Others) was the best foreign language film.
The Spanish-language dark fairytale Pan's Labyrinth won three Academy Awards, for cinematography, art direction and make-up.