Data recovery from WD Elements Hard drive after Time Machine formatted it

I plugged my brother in laws WD Elements hard drive into my MacBook Pro. It asked me if I wished to use this drive as my time machine back up to which I answered no. I was going to copy and paste some movies onto his drive. I not sure how it occurred but Time Machine has now "partitioned or formatted " the drive and erased all data that was on it. The drive appears empty on my MacBook and is now unrecognisable on his PC computer. The drive had some important documents and I am praying that I somehow can recover them. Does anyone have Amy suggestions as to where to start ?? Please help !!!