The 36-year-old from Montreal won the 185-pound crown November 4 when he dethroned Michael Bisping at UFC 217 in NY.
The win was notable not only because it made St-Pierre one of the only fighters to hold a title in two different UFC divisions, but because, even after a four-year vacation from MMA, GSP was able to beat the champion in the division above the one he usually fights in.
"My fight at UFC 217 was one of the greatest nights of my life", he said.
As this is being written, the bout hasn't been announced yet, but it looks like Robert Whittaker and Luke Rockhold will be fighting at UFC 221, February 10th. "Out of respect to the athletes and the sport, I don't want to hold up the division".
Whittaker (19-4), victor of The Ultimate Fighter: Smashes, initially won the interim title with a hard-fought decision over Yoel Romero in July.
He told TSN that he doesn't believe it's healthy for him to compete in a heavier weight class: "We'll talk about it, but I'm not sure if I compete I will go back at 185 [pounds]".
The UFC have confirmed that Australian Whittaker is now officially the holder of the title, and while he has won it without a punch, it won't be long before he is forced to defend it.
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 was his first fight back in the Octagon since losing the belt to Bisping in June 2016.