Multi-component decomposition of the C IV line profile in SDSS J1339+1310A. The profile is decomposed into three Gaussian components: C IV broad + C IV narrow + He II complex. The grey rectangles highlight the two spectral regions that we used to remove a linear continuum under the emission line, and the vertical dotted lines correspond to the centres of the Gaussians. Top panel: GTC-OSIRIS-R500B data in May 2014, while bottom panel: HST-WFC3-UVIS data in February 2016.