For the first time ever, Sheldon Cooper and Amy Farrah shared a kiss, taking their relationship to another level during a special Valentine's Day episode of "The Big Bang Theory" last week.

The unexpected kissed happened in Episode 15 while the couple was on a romantic Valentine's Day train getaway with Howard and Bernadette. However, the ride started to go south because Sheldon was ignoring Amy and began spending time with a random stranger. The pair then got into a heated argument and Sheldon kissed his girlfriend in the heat of the tiff to prove that he was romantic, reports Entertainment Weekly.

Because Sheldon is portrayed as a stubborn, neurotic and socially inept theoretical physicist who is against the idea of physical contact and intimacy, the kiss came as such a major surprise. 

Unfortunately, fans of the popular CBS comedy series will have to wait two weeks for another all-new episode and to see how their kiss will change their relationship.

According to Hollywood Hills, the upcoming episode is entitled "The Table Polarization" and is scheduled to air at the end of the month. Spoiler TV also revealed a casting teaser, stating that "Episode 7.16 of The Big Bang Theory will see the return of Casey Sanders as Mr. Rostenkowski."

Later on in the season, Bob Newhart is slated to make a third appearance on the popular sitcom to reprise his Emmy-winning role as Sheldon and Leonard's childhood Professor Proton, TVLine  reports exclusively.

"The Big Bang Theory" S7E16, "The Table Polarization," will air on Thursday, Feb. 27 at 8 p.m. on CBS.