Aluminum-magnesium isotopic analysis of plagioclase in the eucrite Piplia Kalan, with (27)A1/Mg-24 ratio between 2000 to 7000, reveals the presence of excess magnesium-26 resulting from in situ decay of the short-lived nuclide aluminum-26. This observation confirms aluminum-26 as a plausible heat source for melting and differentiation of the eucrite parent body in particular and for planetesimals in general. The inferred initial abundance of Al-26/Al-27 Of (7.5 +/- 0.9) x 10(-7) indicates that melting, differentiation, and crust formation in the parent body of Piplia Kalan was complete within 5 million years of the formation of the solar system.