In at least two episodes (The High Ground & Attached - maybe another) Crusher and Picard are in life or death situations, and she tells him, "Jean-Luc, I have something to tell you..." A friend speculated that Wes was actually Picard's son from a fling they had when she was still with Jack.
I've heard that one before. In an evil mirror universe maybe – but it's just not believable, in fact it's down right silly, for the characterizations shown in the canon universe. It would mean both Jean-Luc Picard and Beverly Crusher engaging in a rather vile and despicable pattern behaviors. It would entail Picard knocking boots with the wife of his best friend and fellow officer. It would also require Dr. Crusher to lie to her husband and her son about her son's paternity - possibly having to alter medical records. Sorry, I don't see either character behaving in such a manner.