'The Big Bang Theory' season 10 news, spoilers: Premiere episode to highlight 'tension' between all the parents

The season 9 finale of CBS' long-running sitcom "The Big Bang Theory" ended on a major cliffhanger involving Sheldon's (Jim Parsons) mother, Mary (Laurie Metcalf), and Leonard's (Johnny Galecki) dad, Alfred (Judd Hirsch).

The season 9 ender heavily teased that the two had spent the night together after they left to go to the same hotel and turned off their phones for the night, leaving Sheldon and Leonard unable to contact them. The next morning, both were MIA at Penny (Kaley Cuoco) and Leonard's wedding.

In a recent interview with Entertainment Weekly, "Big Bang Theory" executive producer Steve Molaro talked about the season 10 premiere, saying: "We're left with a good amount of tension between all the parents. There's a lot of fallout the following morning before we even get to the ceremony, if we even do."

In May, Molaro spoke to EW about what Mary and Alfred had been up to, saying that he doesn't know what really went down between the two.

"I know they were getting along quite well, and left to go to the same hotel for a nightcap, and turned off their phones," he said. "The details of exactly what happened, if we even ever find out all the details, will be left for the season premiere of season 10."

Molaro also talked about how Sheldon and Leonard will react to the knowledge that their parents hooked up (if that is what they did), saying that "uncomfortable" would be their primary emotion.

The "Big Bang Theory" boss also revealed that the season 9 finale was supposed to feature a joke that referred to Sheldon and Leonard as potential brothers. It was, however, cut from the script.

Nonetheless, should the new season find Mary and Alfred becoming an item and possibly even getting married, Sheldon and Leonard may very well find themselves technically becoming step-siblings.

"The Big Bang Theory" season 10 debuts Monday, Sept. 19, on CBS.