Mary (Laurie Metcalf) and Missy (Courtney Henggeler) had a tense relationship in The Big Bang Theory, and Young Sheldon may have explained the reason why. Long before the CBS prequel spin-0ff was greenlit, the Cooper family was already introduced. Some of them visited Sheldon (Jim Parsons) in Pasadena, with his mom and twin sister both appearing as early as The Big Bang Theory season 1. Young Sheldon builds on certain details first revealed on The Big Bang Theory, such as what really happened the day Sheldon caught his dad having an affair. Admittedly, the prequel has received criticism for its lax approach to continuity, but sometimes, Young Sheldon seizes the opportunity to further explore plotlines about Sheldon and his family that were never fully tackled in The Big Bang Theory.

For example, the spin-off has laid the foundation for Georgie's (Montana Jordan) future as a successful business owner. It has even included several allusions to Sheldon's life in Pasadena surrounded by his loyal friends after spending much of his childhood being anti-social. In light of that, Young Sheldon season 5, episode, titled "Money Laundering and a Cascade of Hormones," may have also revealed why exactly Missy and Mary had a contentious relationship in The Big Bang Theory.

Related: Young Sheldon Hints At Why Mary Never Mentioned George's Affair In TBBT

The events of the outing were kicked off by Missy's (Raegan Revord) countless questions about romantic relationships during Sunday School. This motivated Youth Pastor Rob (Dan Byrd) to convince the Church and Mary (Zoe Perry) that it's time for the kids to be educated about the matter. The Cooper matriarch attempted to do that with the Cooper twins, but while Sheldon (Iain Armitage) was willing to participate, his sister was another story. In the end, Missy got more mad at her mother after news broke out that she's planning on giving a talk at school about the awkward topic. While this was all happening in Young Sheldon, both Missy and Mary were apparently developing a crush on Youth Pastor Rob, as well.

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No one else knows about their separate attraction to the same person. But Young Sheldon showed both characters secretly crushing on their Church's new Youth Pastor. Mary dreamed of actually sleeping with him, and the next time they encountered each other at work, she gave in to her impulses and checked him out. Meanwhile, Missy's attraction wasn't revealed until the closing moments of the episode. As she slept soundly in her room, the spin-off revealed that she was dreaming of getting married to Youth Pastor Rob.

It's uncertain if there's anything significant that will come out of this brand new Young Sheldon plotline. But, for what it's worth, it doesn't seem like their crush on him is fading any time soon. And, in the unfortunate event that they found out about each other's secrets, it's not outside the realm of possibility that Missy fully loses it on her mother. As it is, their relationship is already in a precarious place after the sex talk snafu. But if there's one thing that both The Big Bang Theory and Young Sheldon confirmed about Sheldon's sister, it's that Missy falls in love hard and fast. Learning that her mother is pining for the same man could understandably make her detest Mary more than she currently does.

It's clear that Mary's favorite is Sheldon, while Missy has a closer relationship with her dad. In fact, Missy never badmouthed George (Lance Barber) in The Big Bang Theory while her mother and twin brother always poked fun of the Cooper patriarch. The potential disaster brought about by Mary and Missy's attraction to Youth Pastor Rob in Young Sheldon could very well be what kickstarts their complicated relationship. Aside from Missy not liking the idea of her mom also checking out her crush, she can interpret it as Mary being unfaithful to George.

More: Young Sheldon Explains A Sheldon & Leonard Roommate Mystery From TBBT