Anna Paquin and Stephen Moyer on May 30, 2012 in Hollywood, California. Credit: Jason Merritt/Getty Images

What's in the water on the set of True Blood?

A source confirms to Us Weekly that Anna Paquin, 29, and her husband of nearly two years, Stephen Moyer, 42, are expecting a double delivery in the fall!

"I'm so excited for them," the couple's costar Sam Trammell -- father to 11-month-old twins Winston and Gus with girlfriend Missy Yager -- shared with Us recently when we chatted with him about the double baby news at Planet Hollywood's Gallery Nightclub in Las Vegas. "We sent them a special gift. It's so interesting that True Blood has become, like, the 'twins' show."

And though Moyer has two children, Lilac, 10, and Billy, 12, from a previous relationship, he's been listening intently to Trammell's advice on the ins and outs of raising multiples.

"It's harder, having twins, but it's all we know. So we're trying to impart some decent wisdom," Trammell added. "I told them to hold on tight!"

But Moyer is up for the challenge. "It's always amazing," he told Zap2it in May of his wife's pregnancy. "I love my kids so much. And I think that the fact that Anna is pregnant just adds more crazy to the bundle of fun."