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Hydrogen-deficient central stars of planetary nebula such as Wolf-Rayet andPG1159 central stars and some weak emission line stars are primarily composedof helium and carbon. This abundance is well explained by a scenario where asingle post-AGB star experiences a last helium shell flash which ingests andburns, or simply dilutes, the remaining hydrogen atmosphere. But despite itssuccess in matching the photospheric abundances of these stars, this scenariois faced with several observational challenges. A binary scenario is proposedhere as a more natural way to face some of the most stringent observationalconstraints. In this scenario the H-rich primary in a close binary formedduring a common envelope on the AGB, suffers a last helium shell flash, whichresults in a H-deficient primary with some of the characteristics needed tomatch the observations.

[WC] and PG1159 Central Stars of Planetary Nebula: the Need for an Alternative to the Born-Again Scenario