The identification of active PeVatrons, hadronic particle accelerators reaching the knee of the
cosmic-ray spectrum (at the energy of few PeV), is crucial to understand the origin of cosmic rays
in the Galaxy. In this context, we report on new H.E.S.S. observations of the PeVatron candidate
HESS J1702-420, which bring evidence for the presence of γ-rays up to 100 TeV. This is the
first time in the history of H.E.S.S. that photons with such high energy are observed. Remarkably, the new deep observations allowed the discovery of a new γ-ray source component, called
HESS J1702-420A, that was previously hidden under the bulk emission traditionally associated
with HESS J1702-420. This new object has a power-law spectral slope < 2 and a γ-ray spectrum
that, extending with no sign of curvature up to 100 TeV, makes it an excellent candidate site for
the presence of PeV-energy cosmic rays. This discovery brings new information to the ongoing
debate on the nature of the unidentified source HESSJ1702-420, and on the origin of Galactic
cosmic rays.