My guess would be a Radza son. There are a plethora floating around bachelor holding that could've made the move quietly and the departing facility hasn't announced it. While someone from the Calvin or Motek/Warda lines is a possibility, I still find it an unlikely decision. Charlie Gray may be a controversial figure but I don't think he would be daft enough to import a related bull unless he's shipping cows out.
That being said, this does put ALS in an interesting position. They currently have 8 potential breeding cows with more upcoming. They certainly do not have the barn space for this. With a new bull onsite I have to wonder if this "controversial announcement" has to do with moving some cows from the facility and splitting up some groupings. Many people have speculated that Lily and Emily's matrilines could be shipped out to focus on Natasha's, but it is a possibility that they might be willing to split Natasha and Opal up for whatever reason and that might rear some heads. US facilities like Tulsa and LA would be eager to get cows if they were looking to be offloaded, but if it were an upcoming announcement we should have some inkling of it by now unless they're going to great lengths to keep it hush hush.