Observational abundance analysis, as well as photo-ionization models (Pollaco 1999, Kerber et al. 1999) of the planetary nebula of Sakurai's Object indicate that this peculiar star is a `born-again' AGB star which has experienced a very late thermal pulse during its previous first post-AGB evolution. I will describe the current status of post-AGB stellar modelling. Particular emphasis will be put on the abundance evolution due to mixing and nucleosynthesis related to the different flavours of post-AGB thermal pulses. The potential of different models to reproduce the properties if Sakurai's Object are discussed. New convective nucleosynthesis models of the very late thermal pulse now include the light elements (including 11B) and are able to explain, for example, the enormous lithium abundance found by Asplund et al. (1999). At the same time the models are in qualitative agreement with the low high-mass:low-mass s-process index.