Ashton Kutcher & Lea Michele: Friendly ... or Flirting?

Ashton Kutcher arrived solo last night at the premiere of "New Year's Eve" -- was he flirting with one of his co-stars when he got there?

Kutcher and Lea Michele got mighty close on the arrivals line, posing for a few touchy-feely photos together as Lea held onto Kutcher's head, laughing.

The co-stars are both living the single life now, as Ashton and Demi Moore recently announced their separation following infidelity rumors. Lea also recently split from her boyfriend of a year, Theo Stockman, back in September.

"It was such an honor working with you. I cannot thank you enough," Lea tweeted at Ashton after the premiere.

Check out more photos above -- think they were flirting ... or just acting like a couple of cute co-stars?