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Even though the first fossil group openParFGclosePar was discovered almost three decades ago their origin and evolution still remain unclear. The popular explanation that they are cannibalistic remains of groups that lost energy through dynamical friction is not consistent with their typically lack the expected large cool cores. We have raised a representative sample of FGs with high quality X-ray and optical data and developed a robust technique to estimate their relative age and dynamical stage using the ICL. The inital results have been surprising and highlighted the need to collect data from evolutionary phases prior to FG formation openParFG progenitors or FPsclosePar to understand their origin. Here comma we propose short XMM observations of the 2 brightest and most informative FPs.