It's back on - Jude Law and Sienna Miller let the world know they have reunited

When reports that Jude Law and Sienna Miller had reunited first emerged late last year, the couple insisted they were nothing more than "friends".

But this week the former lovers confirmed what many already suspected and went public with their new relationship – in a very high-profile manner.

Jude and Sienna stepped out together to walk down the red carpet at one of New York's biggest social events by way of debuting their rekindled romance.

The pair joined an impressive list of stars attending the 2010 Costume Institute Gala, where they were keen to show they were very much an item, walking arm in arm as they made their arrival.

Twenty-eight-year-old Sienna held her own against screen beauties including Jennifer Lopez, Anne Hathaway and Kristen Stewart, making an impact in a plunging Emilio Pucci midnight blue gown with a tiered skirt.

And Jude, smart in a black suit, couldn't have looked happier.

It was back in 2005 that the couple ended their engagement after the Alfie actor's infidelities with his children's nanny.

Jude, who has three children, Rafferty, 13, nine-year-old Iris and Rudy, seven, with ex-wife Sadie Frost, also has another daughter, seven-month-old Sofia with model Samantha Burke.

Sienna dated Welsh star Rhys Ifans from 2007 until June 2008, before beginning a controversial relationship with married American actor Balthazar Getty.