updated 08/23/2010 AT 9:00 AM ET
•originally published 08/23/2010 AT 9:35 AM ET
The pair, who’ve been dating quietly for some time, enjoyed their first public outing together on Saturday, walking around London’s trendy Soho and Mayfair districts.
“They’re seeing each other,” a friend of Winslet’s tells PEOPLE. “She’s known him since earlier this year.” Friends point to the happiness she has shown in the photographs as proof of how she’s feeling.