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© H.E.S.S. and MAGIC Collaborations 2021. Artículo firmado por 427 autores. The authors wish to thank the anonymous referee for a constructive report, which helped to improve the manuscript. The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support by the German Ministry for Education and Research (BMBF), the Science and Research and the Austrian Science Fund (FWF)Max Planck Society, the German Research Foundation (DFG), the Helmholtz Association, the Alexander von Humboldt Foundation, the French Ministry of Higher Education, Research and Innovation, the Centre National de la Recherche Scientifique (CNRS/IN2P3 and CNRS/INSU), the Commissariat a l'energie atomique et aux energies alternatives (CEA), the U.K. Science and Technology Facilities Council (STFC), the Knut and Alice Wallenberg Foundation, the National Science Centre, Poland grant no. 2016/22/M/ST9/00382, the South African Department of Science and Technology and National Research Foundation, the University of Namibia, the National Commission on Research, Science & Technology of Namibia (NCRST), the Austrian Federal Ministry of Education, Science and Research and the Austrian Science Fund (FWF), the Australian Research Council (ARC), the Japan Society for the Promotion of Science and by the University of Amsterdam. We appreciate the excellent work of the technical support sta ff in Berlin, Zeuthen, Heidelberg, Palaiseau, Paris, Saclay, Tubingen and in Namibia in the construction and operation of the equipment. This work benefited from services provided by the H.E.S.S. Virtual Organisation, supported by the national resource providers of the EGI Federation. We would like to thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The financial support of the German BMBF and MPG; the Italian INFN and INAF, The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complex multiwavelength behaviour and it is one of only a few FSRQs detected in very-high-energy (VHE, E>100 GeV) gamma rays. The VHE gamma -ray observations with H.E.S.S. and MAGIC in late May and early June 2016 resulted in the detection of an unprecedented flare, which revealed, for the first time, VHE gamma -ray intranight variability for this source. While a common variability timescale of 1.5 h has been found, there is a significant deviation near the end of the flare, with a timescale of similar to 20 min marking the cessation of the event. The peak flux is nearly two orders of magnitude above the low-level emission. For the first time, a curvature was detected in the VHE gamma -ray spectrum of PKS 1510-089, which can be fully explained by the absorption on the part of the extragalactic background light. Optical R-band observations with ATOM revealed a counterpart of the gamma -ray flare, even though the detailed flux evolution differs from the VHE gamma -ray light curve. Interestingly, a steep flux decrease was observed at the same time as the cessation of the VHE gamma -ray flare. In the high-energy (HE, E> 100 MeV) gamma -ray band, only a moderate flux increase was observed with Fermi-LAT, while the HE gamma -ray spectrum significantly hardens up to a photon index of 1.6. A search for broad-line region (BLR) absorption features in the gamma -ray spectrum indicates that the emission region is located outside of the BLR. Radio very-long-baseline interferometry observations reveal a fast-moving knot interacting with a standing jet feature around the time of the flare. As the standing feature is located similar to 50 pc from the black hole, the emission region of the flare may have been located at a significant distance from the black hole. If this is indeed a true correlation, the VHE gamma rays must have been produced far down in the jet, where turbulent plasma crosses a standing shock., Ministerio de Economía y Competitividad (MINECO)/FEDER, Centro de Excelencia Severo Ochoa, Unidad de Excelencia María de Maeztu, German Ministry for Education and Research (BMBF), Max Planck Society Foundation CELLEX, German Research Foundation (DFG), Helmholtz Association, Alexander von Humboldt Foundation, French Ministry of Higher Education, Research and Innovation, Centre National de la Recherche Scientifique (CNRS/IN2P3), Commissariat a l'energie atomique et aux energies alternatives (CEA) French Atomic Energy Commission, U.K. Science and Technology Facilities Council (STFC), Knut and Alice Wallenberg Foundation, National Science Centre, Poland, South African Department of Science and Technology, National Commission on Research, Science & Technology of Namibia (NCRST), Austrian Federal Ministry of Education, Science and Research, Austrian Science Fund (FWF), Australian Research Council (ARC), Japan Society for the Promotion of Science, University of Amsterdam, German MPG, German BMBF Federal Ministry of Education & Research, Italian INFN Istituto Nazionale di Fisica Nucleare, Italian INAF Istituto Nazionale Astrofisica, Swiss National Fund SNF, Indian Department of Atomic Energy, Japanese ICRR, University of Tokyo, JSPS, Japan, MEXT Ministry of Education, Culture, Sports, Science and Technology, Japan, Bulgarian Ministry of Education and Science; National RI Roadmap Project, Academy of Finland European Commission, Foundation La Caixa, Croatian Science Foundation (HrZZ) Project, University of Rijeka Project, DFG Collaborative Research Centers, German Research Foundation (DFG), Polish National Research Centre grant, Brazilian MCTIC, Brazilian CNPq Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brazilian FAPERJ, DOE United States Department of Energy (DOE), NASA National Aeronautics & Space Administration, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub