Abstract
Gamma-ray bursts are usually followed by afterglows produced by synchrotron radiation which makes them detectable out to the far Universe. Here we present the unusual GRB 101225A, also named the ``Christmas burst'', an extremely long γ-ray burst followed by a bright X-ray afterglow and a peculiar optical counterpart. The X-ray spectrum shows an additional thermal component while the UV-optical-IR SED evolves as a cooling, expanding black-body until 10 days, after which a faint supernova emerges. With GTC/OSIRIS, we detect an extremely faint host galaxy 6 months after the burst.
