  Next generation CMB experiments such as CMB-S4 aim at measuring the CMB
lensing potential at sub-percent precision where most of the constraining power
will come from CMB polarization. We investigate the prospects of achieving this
goal in the presence of large-scale, diffuse galactic foreground emission by
using non-Gaussian sky simulations and exploit multi-frequency information to
clean those. We show that, while prior to foreground cleaning, cosmological
parameter estimates from the contaminated lensing potential estimation can be
significantly biased, these can be successfully mitigated by applying a
parametric foreground cleaning approach. We further observe no significant
additional bias in the delensed B-mode power spectrum after applying foreground
cleaning and are therefore able to obtain an unbiased measurement of the
tensor-to-scalar ratio, $r$, after delensing.

Cosmology and Nongalactic Astrophysics