  On May 21, 2019 Advanced LIGO and Advanced Virgo detectors observed a
gravitational-wave transient GW190521, the heaviest binary black-hole merger
detected to date with the remnant mass of 142$\,$M$_\odot$ that was published
recently. This observation is the first strong evidence for the existence of
intermediate-mass black holes. The significance of this observation was
determined by the coherent WaveBurst (cWB) - search algorithm, which identified
GW190521 with minimal assumptions on its source model. In this paper, we
demonstrate the capabilities of cWB to detect binary black holes without use of
the signal templates, describe the details of the GW190521 detection and
establish the consistency of the model-agnostic reconstruction of GW190521 by
cWB with the theoretical waveform model of a binary black hole.
