Scarlett Johansson has become engaged to her actor boyfriend Ryan Reynolds after a one year courtship.

The Lost In Translation actress looked delighted as she showed off her new diamond ring for the first time as she attended the Metropolitan Museum of Art's Costume Institute Gala in New York City last night.

The 23-year-old and Canadian beau Reynolds, 31, started dating in March 2007 - a month after the Just Friends actor ended his three-year engagement to singer Alanis Morissette.

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Rock on: Scarlett Johansson showed off her new engagement ring at last night's Metropolitan Museum of Art's Costume Institute gala in New York

Johansson's representative Marcel Pariseau confirmed the couple's engagement to People magazine on Monday.

She said: "They're both thrilled."

Pariseau declined to say exactly when the couple got engaged, but admitted it was recently. They are yet to set a wedding date.

Johansson initially denied reports in February that the couple were getting married after she was spotted looking at wedding gowns at the Monique Lhuillier boutique in LA.

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Wedding plans: Canadian actor Ryan Reynolds has proposed to the Lost In Translation star

Before she starting dating Reynolds last year, Johansson was in a two-year relationship with her Black Dahlia co-star Josh Hartnett and previously dated actor/singer Jared Leto.

Friends of the couple believe they may delay the wedding until after this year because they are so busy.

Johansson's debut album Anywhere I Lay My Head is released on May 20 and she has two movies Vicky Cristina Barcelona and He's Just Not That Into You coming out this summer.

She is currently filming New York, I Love You in her hometown of NYC, while Reynolds is currently making romantic comedy The Proposal with Sandra Bullock four hours away in Boston.