According to the GBA release on the 5th July (page 2)...
The major shareholders of Advent are as shown below:
MEC Resources (ASX:MMR) 51.14%
BPH Corporate Ltd (ASX:BPH) 19.06%
Talbot Group Investments 10.42%
Grandbridge Limited (ASX:GBA) 8.75%
So I think once you add in GBA's indirect holdings via MMR and BPH their actualy stake in Advent is higher.