  LIGO/Virgo Collaboration reported the detection of the most massive black
hole - black hole (BH-BH) merger up to date with component masses of 85 Msun
and 66 Msun (GW190521). Motivated by recent observations of massive stars in
the 30 Doradus cluster in the Large Magellanic Cloud (>200 Msun; e.g. R136a)
and employing newly estimated uncertainties on pulsational pair-instability
mass-loss (that allow for possibility of forming BHs with mass up to 90Msun) we
show that it is trivial to form such massive BH-BH mergers through the
classical isolated binary evolution (with no assistance from either dynamical
interactions or exotica). A binary consisting of two massive (180+150 Msun)
Population II stars (Z=0.0001) evolves through a stable Roche lobe overflow and
common envelope episode. Both exposed stellar cores undergo direct
core-collapse and form massive BHs while avoiding pair-instability pulsation
mass-loss or total disruption. LIGO/Virgo observations show that the merger
rate density of light BH-BH mergers (both components: <50 Msun) is of the order
of 10-100 Gpc^-3 yr^-1, while GW190521 indicates that the rate of heavier
mergers is 0.02-0.43 Gpc^-3 yr^-1. Our model (with standard assumptions about
input physics) but extended to include 200 Msun stars and allowing for the
possibility of stellar cores collapsing to 90 Msun BHs produces the following
rates: 63 Gpc^-3 yr^-1 for light BH-BH mergers and 0.04 Gpc^-3 yr^-1 for heavy
BH-BH mergers. We do not claim that GW190521 was formed by an isolated binary,
but it appears that such a possibility can not be excluded.
