Fortune, 26, made four appearances for Stoke after being signed as Michael Duberry's replacement. He was largely impressive during that time and will no doubt slip straight back into the back four for the visit of Southampton on Saturday.
Assistant City boss Dave Kemp told the official Stoke Website, "We are delighted to have him back, we never wanted to lose him in the first place.
"He was exceptional for us before and hopefully he can do exactly the same this time around."