GTC spectrum of the transient in the SN 2019zbq host galaxy, taken on 4 December 2019. Vertical dotted lines give the locations of sky lines and tellurics. Top: Extracted spectra at the centre of the trace (host + excess) and at the side of the extended host galaxy trace (host). The sharp decline around 9000 Å is due to the low sensitivity of the detector at these wavelengths, and has been used to scale the spectra such that their difference goes to 0. Bottom: The difference of the two spectra in the top panel, showing the isolated spectrum of the excess. The host spectrum has been re-scaled to ensure that the red edge is the same for both spectra.