After letting the cat out of the bag and revealing that Penny and Leonard will indeed get married in the Season 9 premiere of "The Big Bang Theory," the showrunner has now opened up about what's to come for the newlyweds and how Leonard's confession about kissing another woman will affect their relationship.

During the Season 8 finale, Penny and Leonard agreed to elope in Las Vegas. However, Leonard started having second thoughts and confessed to Penny that he had kissed another woman when he was drunk on a North Sea expedition a few years ago. Penny assumed that he told her this in order to sabotage their plans to wed, but Leonard assured her that he's totally committed to the idea, so they agree to go through with it.

Despite their hang-up, executive producer Steve Molaro confirmed that the couple will tie the knot in the Season 9 premiere. However, he said, "That's really only the beginning of the story. As fun and as great as it is to see them get married, that's only part of it," reports TVLine.

This could be a hint that the newlyweds will experience trouble when Leonard's new wife comes face-to-face with his "other woman," who will be played by "Mom" star Melissa Tang, according to TVLine. As a result, this could put a damper on Leonard and Penny's potential honeymoon.

In a recent interview with The Hollywood Reporter, Molaro said that the time was right for the couple to take the next step in their relationship.

"It's season nine and Leonard has been pursuing her since minute three of the series," he said. "Even Penny, with all of her commitment issues, is in a mindset of, 'Are we moving forward with this or not? What are we doing?' And they do."

The EP also teased that Penny may not be as cool as she thinks she is about Leonard's confession.

"She thinks she's OK with it and she may not be," he said.

"It's the kind of thing that you wouldn't expect to happen and that can be a little jarring. I think when you're Penny, and you have an image that you've cultivated of a person for eight years now and those two things aren't aligning anymore -- that can be a difficult thing to deal with."

The couple will also face "quite a challenge" on their wedding night, Molaro teased.

Later on in the series, Leonard will try to bring the issue to rest by confronting the woman he kissed, Mandy.

"Leonard will speak to her in a desperate attempt to put this fire out. This all goes down in the second episode. The topic of Leonard talking to Mandy or Penny talking to her or the three of them talking to each other comes up. The thought of maybe somehow interacting with her that this can all be put to bed is the impetus behind it," the showrunner said.

When asked why he chose to reveal that Penny and Leonard will officially say "I do" in the season premiere, Molaro explained that they didn't want fans to think that they were pulling the rug over their eves again.

"Chuck and I had a long talk about [revealing the wedding before the premiere] and my fear was that it was going to start sound like they didn't [get married]," Molaro said. "That was not a positive message - and we didn't want fans to feel like, 'Oh, they're going to pull the rug again and not do it.' There is so much more story beyond that moment that we decided to just let people know."

In light of the season premiere, which is set to premiere on CBS on Sept. 21, the show released a new promo video featuring a flashback of the moment when Leonard first saw and fell for Penny.

Watch the promo below.