Big Bang Theory season 9 finale
Everyone gathers for a family dinner in The Big Bang Theory season 9 finale pictures CBS

The Big Bang Theory season 9 ended on a bit of a romantic cliffhanger on whether Sheldon's mother Mary Cooper and Leonard's father Alfred Hofstadter hooked up or not.

The finale episode kicked off with Leonard and Penny inviting their respective families and Sheldon's mother Mary for a small "re-wedding". Leonard's decision to invite his father didn't bode too well with his mother Beverly, as the divorced couple spent the entire evening throwing curses at each other and making the situation awkward for everyone.

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However, the surprise of the evening was Mary and Alfred hitting it off, thanks to their common hatred for Beverly. At the dinner party, after a rather bitter wordplay with his ex-wife, Alfred decided to retire for the night and Mary too joined him, as it turned out that both of them were staying in the same hotel.

The episode ended with Sheldon trying to call his mother and Leonard texting his father, while both of them did not respond. Penny snidely remarked: "Because they both turned their phones off," hinting that they might be spending the night together.

Executive producer Steve Molaro spoke to Entertainment Weekly about the season 9 finale cliffhanger. According to him, the details about Alfred and Mary's night will be revealed in the season 10 premiere episode.

Molaro said: "I don't know what happened. I know they were getting along quite well, and left to go to the same hotel for a nightcap, and turned off their phones. 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."

When asked about Sheldon and Leonard being "potential brothers" next season, the producer shared: "It's inching toward that, isn't it? There was — it fell out of the script — a joke referring to them as potential brothers. I'm going to go with the word "uncomfortable" probably is a good starting place for their primary emotion of where we leave them and where we will pick up."

Season 10 of The Big Bang Theory will pick up immediately after the events of the season 9 finale, according to Moralo. CBS is yet to release the premiere date for TBBT's 10th season.