Sheldon (Jim Parsons) is planning something huge for Amy's (Mayim Bialik) birthday celebration in the upcoming episode of "The Big Bang Theory."

In the episode titled "The Birthday Synchronicity," the promo reveals that "Shamy" will try to uphold their promise to be intimate once a year on Amy's birthday. In the clip, the two look cozy in their bed and are starting to set the mood when excited shouts are heard coming from their friends. Bernadette (Melissa Rauch) is reportedly about to give birth and everyone is going to the hospital to visit. Suffice to say, Amy is not happy that her birthday gift from Sheldon is on the verge of getting postponed.

The teaser shows Amy teasing Sheldon with her "Harry Potter" costume. As the couple exchange kisses, Leonard (Johnny Galecki) and Penny (Kaley Cuoco) shout that Bernadette's water broke and that they are on their way to see her. Amy is so incensed that she cannot stop herself from shouting back that it was wrong timing. Amy's birthday "gift" was planned when she had her celebration last year. After a successful romp, Sheldon said he liked it and that they should do it annually.

Executive producer Steve Molaro previously talked to Variety about the "Shamy" promise.

"As far as this being some sort of sellout or giant shift in the character, I think it's lines like that that allow us to have such a momentous occasion, but it still can feel very much like Sheldon and Amy — Sheldon saying that we did this thing, but we're only going to do it once a year is an example of us holding the character intact, even when something this monumental happens," the EP explained.

"The Big Bang Theory" season 10 episode 11 airs Thursday, Dec. 15 at 8 p.m. EST on CBS.