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We present new HST/WFC3 observations and re-analyse VLT data to unveil thecontinuum, variability and rest-frame UV lines of the multiple UV clumps of themost luminous Ly$\alpha$ emitter at z=6.6, CR7. Our re-reduced, flux calibratedX-SHOOTER spectra of CR7 reveal a HeII emission line in observations obtainedalong the major axis of Lyman-alpha (Lya) emission with the best seeingconditions. HeII is spatially offset by +0.8'' from the peak of Lya emission,and it is found towards clump B. Our WFC3 grism spectra detects the UVcontinuum of CR7's clump A, yielding a power law with$\beta=-2.5^{+0.6}_{-0.7}$ and $M_{UV}=-21.87^{+0.25}_{-0.20}$. No significantvariability is found for any of the UV clumps on their own, but there istentative (~2.2$\sigma$) brightening of CR7 in F110W as a whole from 2012 to2017. HST grism data fail to robustly detect rest-frame UV lines in any of theclumps, implying fluxes <2x10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ (3 $\sigma$). Weperform CLOUDY modelling to constrain the metallicity and the ionising natureof CR7. CR7 seems to be actively forming stars without any clear AGN activityin clump A, consistent with a metallicity of ~0.05-0.2 Z$_{\odot}$. Component Cor an inter-clump component between B and C may host a high ionisation source.Our results highlight the need for spatially resolved information to study theformation and assembly of early galaxies.

On the nature and physical conditions of the luminous Lya emitter CR7 and its rest-frame UV components