  The Giant Stellar Stream (GSS) is a prominent tidal feature in the halo of
the Andromeda Galaxy (M31), representing the ongoing destruction of a satellite
galaxy. In this paper, we investigate the formation of the GSS through detailed
numerical simulations of the tidal disruption of a progenitor system. Assuming
that the stream was created in a single merger event between M31 and a dwarf
spheroidal galaxy with stellar mass of $10^{9}M_{\odot}$, we successfully
reproduce the dynamical properties of the GSS. As the metallicity distribution
along the stream has been well determined from the observations (PAndAS and
AMIGA data sets), we use Monte Carlo simulations to reconstruct the original
metallicity distribution of the dwarf progenitor. We find that a progenitor
dwarf galaxy with a negative radial metallicity gradient, $\Delta$FeH = -$0.3
\pm 0.2$, reproduces the observed GSS properties at a time between 2.4 and 2.9
Gyrs into the merger. We also show that the observed double peak metallicity
distribution along the stream is a transitory structure caused by unique merger
circumstances where two groups of streaming stars are moving in opposite
directions, intersecting to produce the peaks.
