The two children we mentioned above are twins of the second "generation" of Vision and Wanda, now before that, they are Tommy and Billy.
Their way of birth is the same, the difference is their fate. It is known that Wanda used Mephisto's power to give life to Tommy and Billy.
Finally, Mephisto absorbed his strength again, making the two twin sons of Vision and Wanda disappear. The impact, Wanda was very depressed, and affected her mentally
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