Ryan Phillippe is reportedly dating Amanda Seyfried.

The Hollywood heartthrob and the 'Mamma Mia!' star were spotted out together at Kate Hudson's Halloween party in Los Angeles on Saturday night (30.10.10) and sources nearby claim the pair are "obviously" a couple.

A paparazzi photographer told X17Online: "Ryan and Amanda were definitely together but they didn't really want us photographers to see it.

"Before they realised we were around, they were laughing and chatting with other people at the party and were obviously a couple.

"Ryan was really sweet with her - he had his hand on her lower back for a while when they were talking to another couple. They looked great together."

While Amanda - who until earlier this year was dating British actor Dominic Cooper - took the opportunity of the spooky holiday to dress up as a dog on a lead, Ryan chose to dress down in a simple brown hooded jacket and white t-shirt.

Other celebrities to attend the Hollywood party included Nicole Richie, Leonardo DiCaprio - who remained hidden by a baboon mask - Gwen Stefani and Kurt Russell.