  We perform 3D hydrodynamics simulations of disc-disc stellar flybys with
on-the-fly Monte Carlo radiative transfer. We show that pre-existing
circumstellar discs around both stars result in fast rising ($\sim$yrs)
outbursts lasting 2-5 times longer than for a star-disc flyby. The perturber
always goes into outburst ($\dot{M}>10^{-5}~{\rm M_{\odot}~ yr^{-1}}$). Whereas
we find that the primary goes into a decades long outburst only when the flyby
is retrograde to the circumprimary disc rotation. High accretion rates during
the outburst are triggered by angular momentum cancellation in misaligned
material generated by the encounter. A large fraction of accreted material is
alien.
