It’s the storyline all Big Bang Theory fans have been waiting for – Sheldon Cooper and Amy Farrah Fowler consummating their relationship. Or as Jim Parsons says, “putting the bang into the theory.”

After five years of dating, Parsons and Mayik Bialik’s characters Sheldon and Amy will finally have sex. They're now opening up about it in an on-set interview with ET.

“I was very surprised," Parsons admitted of the storyline. "But then I read it, and it seemed absolutely the right time."

Bialik added, "I was kind of nervous when I first saw where it was going – that it was going to feel voyeuristic or kind of icky, but it’s very tender. It’s very sweet.”

The episode will air on Dec. 17, which will show Sheldon giving Amy a birthday gift to remember.

Parsons described filming the scene as “fun,” and Bialik said it surprisingly wasn’t “icky.”

“I never really thought it would be icky, I don't know why she says that. That may be a personal commentary,” Parsons laughed.