  We measure the evolution of the rest-frame $NUV-V$ colors for early-type
galaxies in clusters at $0<z<1.1$ using data from the Hyper Suprime-Cam Subaru
Strategic Program (HSC-SSP), CFHT Large Area U-band Deep Survey (CLAUDS) and
local SDSS clusters observed with GALEX. Our results show that there is an
excess in the ultraviolet spectrum in most quiescent galaxies (compared to the
expectations from models fitting their optical/infrared colors and spectra)
below $z\sim0.6$, beyond which the excess UV emission fades rapidly. This
evolution of the UV color is only consistent with the presence of a highly
evolved, hot horizontal branch sub-population in these galaxies (amongst the
majority cool and optically bright stars), comprising on average 10\% of the
total stellar mass and forming at $z>3$. The blue UV colors of early-type
galaxies at low-intermediate redshifts are likely driven by this sub-population
being enriched in helium up to $\sim44\%$. At $z>0.8$ (when the extra UV
component has not yet appeared) the data allows us to constrain the star
formation histories of galaxies by fitting models to the evolution of their UV
colors: we find that the epoch at which the stellar populations formed ranges
between $3<z_{form}<10$ (corresponding to $0.5-2.2$ Gyrs after the Big Bang)
with a star-formation e-folding timescale of $\tau=0.35-0.7$ Gyr, suggesting
that these galaxies formed the majority of stars at very high redshift, with a
brief yet intense burst of star-formation activity. The star formation history
and chemical evolution of early-type galaxies resemble those of globular
clusters, albeit on much larger scales.
