Sienna Miller has been getting cozy with Hayden Christensen.

The "Star Wars" hunk has been comforting the 24-year-old actress after she split from Jude Law - again.

Sienna and Hayden have become close while filming new movie "Factory Girl" together and were spotted getting cozy at a cast party on Monday (23.01.06).

An onlooker said: "Sienna and Hayden aren't doing a very good job of keeping their flirtations a secret."

Another partygoer added: "Everybody has been talking about it for a while and after the cast party they were acting like more than good friends."

Revelers also witnessed the pair getting romantic and singing to each other during an impromptu karaoke session.

A source said: "The party was just getting going when someone brought out the restaurants karaoke player - Sienna was on it in a flash."

"She started jokily serenading Hayden before begging him to join her on stage - and it wasn't long before he complied.

"They'd had a fair few drinks by this time and their flirting was obvious to everyone."

"Layer Cake" star Sienna recently split with on/off boyfriend Jude Law. The pair only recently got back together after he apologized for sleeping with the couple's nanny.