The actress ended her on/off relationship with the Brothers & Sisters star earlier this year (09) and has already been linked to the DJ - real name George Barker.
The pair was spotted getting close to one another at the Secret Garden Party in Cambridge, England last month (Jul09), reports Britain's Daily Mirror.
And the 27 year is old is so smitten with the mixmaster, she is already planning their first romantic getaway.
A source tells the newspaper, "Sienna and George is still a pretty casual thing but they're both really happy. George is a good, all-round guy and they have friends in common. He's not famous and isn't interested in fame.
"George is really into his music and has been introducing Sienna to new stuff, and even given her a go on his decks. They've talked about a holiday together and Ibiza has been discussed. It's early days but things are looking great.".