Anna Paquin and True Blood costar (and fiancé) Stephen Moyer
08/25/2009 AT 04:25 PM EDT
They started dating two years ago, but newly engaged
couple Anna Paquin and Stephen Moyer have never let their romance adversely affect their work on True Blood
, says costar Carrie Preston.
"They got together during the pilot although they kept it very quiet," Preston told PEOPLE Monday night at the Nylon
magazine Fall TV & Fashion issue party that Paquin hosted. "I didn't know about it until way into the season. They were very cool and professional about it."
Moyer also attended Monday's event, held at Skybar in the Mondrian Hotel in West Hollywood. He was joined by much of the True Blood
cast, plus celebs such as Eliza Dushku, Emma Roberts, Shannon Elizabeth, Rick Fox and Entourage
's Kevin Connolly.
Moyer, 39, and Paquin, 27, spent much of the evening chatting up friends – many of whom gushed over Paquin's ring. But they also made time for each other, with Moyer hugging Paquin tight as she nuzzled close and whispered in his ear.
On True Blood
, Moyer and Paquin are involved in a love triangle with Alexander Skarsgard
's character. Preston says their real-life romance only makes their performances stronger.
"I certainly think they are more comfortable with each other," Preston says. "Especially in the more intimate scenes."