Somebody earlier mentioned steroids.
To me, he does appear to be holding an artificial amount of muscle, but nothing too crazy. He is a millionaire and could achieve that appearance with excellent genetics (which he has to an extent) and expensive supplementation and diet, so no accusations from me.
If someone were to ask what he was taking, if I had to guess... Looks like test and turinabol, with supplemental GH. Maybe test, deca + proviron. Swollen but not holding enough water or bloat for dbol, not lean/vascular enough for tren or masteron. Winstrol is a no way obviously. Maybe EQ but that has fallen out of favor, even though it is an excellent compound and is one of the few AAS that can offer benefits to endurance-related activities.
Is he still regularly tested? Either way, he's at least staying in shape in a context, and can't be too far away from fighting condition if he ever does return.