LATED: JWST integral field spectroscopy of a galaxy caught in chemical infancy at z=4.8 behind Abell 2744

When Population III (Pop III) star formation ended remains an open question. LATED-1 is an intrinsically faint (M UV=-16.15) Ly α emitter at z=4.80 revealed by VLT/MUSE behind the lensing cluster Abell 2744 (z=0.308). Before any spectroscopic metallicity constraints, it was identified as an extremely metal-poor or metal-free galaxy candidate from JWST imaging by LATED, our novel photometric selection framework. Here we present serendipitous JWST/NIRSpec PRISM integral-field spectroscopy of this target. The spectrum reveals Ly α, H β, and H α at 7.0, 5.6, and 17.7 σ, as well as tentative detections of [O III] λ lambda4959,5007 at 2.9 σ, and yields R3=[O,III] lambda5007/Hβ=0.59+0.27-0.21, upholding the earlier LATED photometric prediction of R3<1.54 (2σ limit). The canonical JWST-based strong-line calibration, extrapolated to low metallicity, implies (O/H)=6.45+0.17-0.19, or Z/Z=0.58-0.20+0.28%, placing LATED-1 among the most metal-poor galaxies known. Its modest magnification (μ=2.80) leaves the intrinsic properties insensitive to the lens model. LATED-1 is therefore a dwarf galaxy caught in the earliest state of chemical enrichment, and a compelling target for testing whether Pop III star formation can persist to z<5. The result demonstrates that photometric selection, especially through the LATED methodology, can reach below one per cent solar metallicity to identify Pop III galaxy candidates for spectroscopic follow-up.