UFC president Dana White installed a clause in St-Pierre's contract upon his return, mandating that if he beat Bisping for the title, he must defend it. St-Pierre notably avoided questions about defending the title in the immediate afterglow of winning the title in November.
The middleweight division will move forward without Georges St-Pierre at the helm.
"Of course, in terms of weight, if I want to go back to compete at 185, obviously eating, like I did what I did, I learned from my mistakes", GSP said.
As a result of the situation, St-Pierre becomes the first fighter in UFC history to vacate championship belts on two occasions.
Rockhold will get the opportunity the reclaim the title he lost to Bisping by shocking first round knockout at UFC 199.
The UFC officially announced the news late Thursday in a press release, which included comment from St-Pierre. He will defend the crown February 10 in Perth, Australia, against former titleholder Luke Rockhold in the main event of UFC 221.
Whittaker (19-4) won the interim championship in July by defeating Yoel Romero via unanimous decision.
Rockhold (16-3), also the former Strikeforce champion, is coming off a dominant second-round submission win over WSOF champion David Branch in September. It should be interesting to see how GSP's new career with the UFC progresses.