Age versus metallicity of the GCs. Coloured dots refer to the MUSE GCs analysed here. The red cross shows the result from the stacked GC spectrum of Fensch et al. (2019), and the blue cross refers to the UDG itself as determined from an aperture spectrum. The dark red point shows the result from the stacked Keck spectra from van Dokkum et al. (2018c), and the green triangle shows the UDG metallicity from slit spectroscopy presented by Ruiz-Lara et al. (2019).