Group Diane was a former special forces unit of the Belgian Gendarmerie (1974-1976), later known as SIE/ESI. After the dissolution of the Gendarmerie SIE/ESI was later renamed to CGSU (Direction Special Units, but now under the supervision of the Commissioner-General of the federal police, hence CGSU) As of now it has been renamed once more to DSU (Direction Special Units, within the general direction support of the federal police)
References
Group Diane Wikipedia(Text) CC BY-SA