Question: What two kickboxing organizations did the brother of Valentin Overeem hold titles in at the same time?
Sentence (from "Alistair Overeem"): He is a former Strikeforce Heavyweight Champion, DREAM Interim Heavyweight Champion, K-1 World Grand Prix Champion, and is one of only two fighters to hold world titles in both MMA and K-1 kickboxing at the same time.
Relevant evidence: Yes