Actress Emily Blunt, who is playing an FBI agent in her upcoming film `Sicario", says she can't talk about her former boyfriend and singer Michael Buble's infidelity rumours as it is `complicated`.

The actress, who is now married to actor John Krasinski, revisited her relationship with Buble on Wednesday when she sat down with Howard Stern for his SiriusXM radio show, reports dailymail.co.uk.

When the host asked about the alleged cheating, the 32-year-old star, who dated Buble for three years between 2005-2008, said `I don't know. It's complicated.`

She added: `I never want to talk about it. I can't do it.`

The actress said that they "had a great time" together and she still has fond memories of the time spent together.

Blunt married Krasinski in 2010 and they share 19-month-old daughter Hazel together. And Buble is now married to Argentine actress Luisana Lopilato and they have a two-year-old son together, Noah and are currently expecting their second child.