  Based on their stellar parameters and the presence of a mid-IR excess due to
circumstellar dust, RV Tauri stars have been classified as post-AGB stars. Our
recent studies, however, reveal diverse SEDs among RV Tauri stars, suggesting
they may occupy other evolutionary channels as well. The aim of this paper is
to present the diverse SED characteristics of RV Tauri stars and investigate
their evolutionary nature as a function of their SEDs. We carried out a
systematic study of RV Tauri stars in the SMC and LMC because of their known
distances and hence luminosities. Their SEDs were classified in three groups:
dusty (disc-type), non-dusty (non-IR) and uncertain. A period-luminosity-
colour (PLC) relation was calibrated. The luminosities from the PLC were
complemented with the ones found using their SEDs and the stars were placed on
the HR-diagram. The four main results from this study are: 1) RV Tauri stars
with a clear IR-excess have disc-type SEDs, which indicates that the dust is
trapped in a stable disc. Given the strong link between disc-type SEDs and
binarity in the Galaxy, we postulate that these are binaries as well. These
cover a range of luminosities and we argue that the more luminous ones are
post-AGB stars while the lower luminosity ones are likely post-Red Giant Branch
(post-RGB) stars. 2) Two of these objects have variable mean brightness with
periods of 916 and 850 days, respectively, caused by variable extinction during
orbital motion. 3) The non-dusty RV Tauri stars and the objects with an
uncertain SED evolve such that the circumstellar dust has dispersed. If they
are single stars, they are post-AGB objects of low initial mass ($<$ 1.25
M$_\odot$), while if they are binaries, the low-luminosity part of the sample
are likely post-RGB stars. 4) We find that RV Tauri stars with dust are on
average more luminous than the rest of the sample.
