User blog comment:Lauren Darkmore/The RWBY AMA on Monty's twitter/@comment-16502426-20131113040316/@comment-86.166.215.41-20140801140737

Monty confirmed that Summer Rose/ Mysterious white cloak (As we all got fond of calling her) is Ruby's mother, which means that Yang and Ruby share a father, but not a mother.

P.S

I was sorta hoping Summer was a long lost sister,