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The flat spectrum radio quasar (FSRQ) PKS 1510-089 is known for its complexmultiwavelength behavior, and is one of only a few FSRQs detected at very highenergy (VHE, $E>100\,$GeV) $\gamma$-rays. VHE $\gamma$-ray observations withH.E.S.S. and MAGIC during late May and early June 2016 resulted in thedetection of an unprecedented flare, which reveals for the first time VHE$\gamma$-ray intranight variability in this source. While a common variabilitytimescale of $1.5\,$hr is found, there is a significant deviation near the endof the flare with a timescale of $\sim 20\,$min marking the cessation of theevent. The peak flux is nearly two orders of magnitude above the low-levelemission. For the first time, curvature is detected in the VHE $\gamma$-rayspectrum of PKS 1510-089, which is fully explained through absorption by theextragalactic background light. Optical R-band observations with ATOM reveal acounterpart of the $\gamma$-ray flare, even though the detailed flux evolutiondiffers from the VHE ightcurve. Interestingly, a steep flux decrease isobserved at the same time as the cessation of the VHE flare. In the high energy(HE, $E>100\,$MeV) $\gamma$-ray band only a moderate flux increase is observedwith Fermi-LAT, while the HE $\gamma$-ray spectrum significantly hardens up toa photon index of 1.6. A search for broad-line region (BLR) absorption featuresin the $\gamma$-ray spectrum indicates that the emission region is locatedoutside of the BLR. Radio VLBI observations reveal a fast moving knotinteracting with a standing jet feature around the time of the flare. As thestanding feature is located $\sim 50\,$pc from the black hole, the emissionregion of the flare may have been located at a significant distance from theblack hole. If this correlation is indeed true, VHE $\gamma$ rays have beenproduced far down the jet where turbulent plasma crosses a standing shock.

Observation of a sudden cessation of a very-high-energy gamma-ray flare in PKS 1510-089 with H.E.S.S. and MAGIC in May 2016