Which is correct?

[Passionwagon]

"It's a mystery what happened to her."

Or

"It's a mystery about what happened to her."


I know that "What happened to her is a mystery", but what I want to know is, in terms of grammar, which is correct. :)

[Mariner]

"It's a mystery about what happened to her."
is certainly wrong.

As for "It's a mystery what happened to her.", I would prefer it like this:
"What happened to her is a mystery"

EDIT:"It's a mystery about what happened to her." would be correct, if you use it as e.g. a narration for a mystery movie. "It's a thrilling movie, a mystery about what happened to her". Still, sounds bit strange though

[Passionwagon]

Thanks for your reply Mariner!

The first one does sound odd, but the reason why I asked is because you can say (I think): There is a mystery about her birthplace.

[Mariner]

True, but notice the difference: "There is a mystery" vs "It is a mystery".