It is not often that one finds natural hybrids and it is even more rare to see them growing cheek by jowl with both parents.
Both parents are widely distributed in the western part of South Africa. T. paniculatus is reported to flower between November and January, and T. wallichii from December through February. This overlap in distribution as well as in flowering period would explain the opportunity for hybridising.
When you have a good look at the picture, you will see that both T. paniculatus and the hybrid are pushing out inflorescences. The plants were photographed on 11 September 2010 (at the eastern side of Skitterykloof), so apparently the flowering period of T. paniculatus is rather longer than indicated in the literature.