Cate Blanchett is "besotted" with her new baby daughter.

Cate Blanchett

Cate Blanchett

The 45-year-old actress and her husband Andrew Upton, who already have three sons, adopted newborn Edith just over a week ago from the US and are totally in love with the tiny bundle of joy.

Speaking to Fairfax Media at the Australian premiere of her new film, Cinderella, last night (14.03.15), she said: "There's a lot of children out there that don't have the good fortune of our biological children so it's lovely to welcome a little girl. We're besotted."

The couple - who have been married since 1997 - are planning to relocate to the US with Dashiell, 13, Roman, 10, Ignatius, six, and little Edith once Andrew's term as the artistic director at the Sydney Theatre Company wraps up at the end of the year.

Andrew, 49, explained: "We're all looking forward to spending more time together in one place. We spent nine years living in England and we loved it. But now we'd like to try America.

"They have terrific [opportunities in] television there and Cate has a very strong film career there, too, obviously."

The Oscar-winning actress first sparked rumours she had become a mother for the fourth time after she was spotted holding the newborn onboard a flight from LAX to Sydney on March 7.