The heavy fermion physics arises from the complex interplay of nearly localized 4f/5f electrons and itinerant bandlike ones,yielding heavy quasiparticles with an effective mass about 100 times (or more) of the bare electrons.Recently,experimental and theoretical investigations point out a localized and delocalized dual nature in actinide compounds,where itinerant quasiparticles account for the unconventional superconductivity in the vicinity of a magnetic instability.Here we report the strong coupling between localized 5f moments and itinerant quasiparticles in the ferromagnetic superconductor UGe2.The coupling is nearly antiferromagnetic.As embedded in the ferromagnetic matrix of localized 5f moments below Tc ≈ 52 K,this coupling leads to short-range dynamic correlations of heavy quasiparticles,characterized by fluctuations of magnetic clusters.Those cluster-like spins of itinerant quasiparticles show a broad hump of magnetization at Tx ≈ 28 K,which is typical for the spin-glass freezing.Thus,our results present the direct observation of itinerant quasiparticles coexisting with localized 5f moments by conventional magnetic measurements,providing a new route into the coexistence between ferromagnetism and superconductivity in heavy fermion systems.