Thor, the Asgardian God of Thunder became a Goddess last year but her identity was kept under the wraps, till now. Thor became a Goddess in a rebooted Thor #1 but Thor's identity will be released in Thor #8.
The new Thor is in fact, Jane Foster who has been appearing in the comics since 1962. Foster is the love interest of Dr. Donald Blake, originally Thor's alter ego.
Recently when Foster appeared in the comics she had been diagnosed with breast cancer and was receiving chemotherapy. Thor writer Jason Aaron told the Times "The very act of picking up this hammer, of becoming Thor is killing her."