9. She Maybe Had A Brother
A lot of Black Widow's life from before she was taken in by the Black Widow program is unknown. Apart from the fact that she may be descended from the Romanov royal family, not much else has been revealed.
The series Shadows and Light did reveal a bit about her family life though. The comic was an anthology series containing the adventures of numerous heroes, all drawn in black and white.
In the story Free Fall, Natasha fought a supervillain called Vindiktor who claimed to be her brother. According to him, Natasha was saved by their mother from a house fire that seemingly killed the rest of the family. Vindiktor had survived though and swore revenge on the sister who he felt had left him to die.
He was killed by Black Widow and the end of the story and was never mentioned again. The problem is that it was later revealed that Natasha had actually been around since the 1940's (a modified version of the super-soldier serum has kept her young over the decades), a plot point that would completely contradict the idea of her having a brother who wasn't an old man by that point.