Stephen Moyer, Anna Paquin and Alan Ball
Sara De Boer/Retna
"I know that they think that nobody knew about it until the end of the season," Ball tells PEOPLE at the 5th annual GLSEN Respect Awards in Los Angeles, "but I knew about it by episode two."
Ball, 52, sensed a connection between the stars after filming the scene where their characters first meet. "Stephen comes into the bar, and takes [Anna's] hand, [and] I thought, "Wow, they have chemistry!" But sometimes actors have chemistry when they're acting together, but they cannot stand each other while off set."
Not the case here, it turns out, of course.
"When I found out that they were dating," Ball says, "my reaction was, 'Uh-oh! I hope that this doesn't blow up in our face.' "
"But this has been happening long enough that it's very clear that it is the real thing," he says of the engaged duo. "They're very, very happy, and I'm just thrilled for them."
