The first solar proton event of solar cycle 25 was detected on 28 October 2021 by several neutron monitors (NMs) in the polar region; the strongest signal was registered by the DOMC/DOMB monitors located at the Antarctic plateau at Concordia French-Italian research station, as well as the fleet of space-borne instruments. It is identified as the GLE (ground-level enhancement) $\#$ 73 in the International GLE database. Here, we report the observations and the study of this event on the basis of the global NM network and SOHO/ERNE records. We present the derived angular and spectral features of solar energetic protons, including their dynamical evolution throughout the event employing a state-of-the-art model based on analysis of the neutron monitor data. We discuss the origin of the prompt and delayed components of the GLE-inducing solar protons. Several applications of the derived results are discussed.