Rick and Morty answered a major question fans had about Rick Sanchez's past with the premiere episode of Season 5! The much anticipated debut of the Adult Swim animated series took things a new step forward for Rick by introducing his nemesis, Mr. Nimbus. But unlike many of the enemies and characters we have seen from Rick's past with the previous four seasons, Mr. Nimbus had an actual impact on Rick as it was clear that Rick was not only agitated at the thought of confronting him but the two of them had a much deeper connection than Rick wanted to admit.
It's soon revealed that their connection goes back quite a bit into Rick's past as a bit of their dialogue seemingly confirms and finally answers the question as to whether or not the mysterious "Diane Sanchez" seen during the third season was in fact Beth's mother. So while Rick had seemingly crafted a fake backstory in order to get the better or the Galactic Federation, Mr. Nimbus' connection to Rick and Diane has cemented that at least part of this backstory is true in some way.
The fifth season premiere, "Mort Dinner Rick Andre," sees Mr. Nimbus declare war on the surface world after their peace treaty talks fall apart (something Rick had been attempting to avoid the entire time), and soon their argument gets a little more personal as Nimbus revealed that Rick and he were once very good friends. He mentions how sad he is to see Rick in his current depressed and lonely state (something previous seasons have been touching on), and then says "If Diane were alive today, what would she think?"
Rick then gets even angrier and meta-jokingly tells Nimbus to stop establishing "canonical backstory," and while this could be a jab at fans looking for character canon like this, Mr. Nimbus' addition to the series seems a bit more concrete. While ridiculous, Rick's attitude towards him further emphasizes how this is really his true nemesis and one that goes back very far in Rick's past and further connects the dots back to Diane Sanchez.
It may not yet be a confirmation of how Diane died as seen in his fabricated origin in the third season premiere, it is a confirmation that Diane Sanchez existed in some form. It's a pretty big step forward for a series that doesn't want to tie itself down with a set canon. But what do you think? Do you think this Diane mention is enough to confirm her existence? Let us know your thoughts in the comments! You can even reach out to me directly about all things animated and other cool stuff @Valdezology on Twitter!