When we went in 2011, there were various things you could pay extra for - cub contact, ambassador encounter, etc.....we went for the cub encounter, and one of them was a king. There was also an adult King in the drive-through cheetah enclosure with 3 'normal' cheetahs.
Definitely an really interesting place...........did you manage any other 'zoos' while in SA? I realise thats not the reason for going though!
We went to an Elephant sanctuary round the corner.
Also went to a small zoo attached to an aquarium up in Hartbeesport near De Wildt - these had an odd mix of fish reptiles birds of prey and random other stuff...few small carnivores too!
We went in Summer 2009 yeah think we paid extra for the ambassador cheetah experience as well was watching one of them run and doing the whole trip round. This was the only king we saw that I remember - I don't have pictures of any others either so think was just this one. They may have bred or had more in since I went