We present the first detailed analysis of the East Cloud , a highly disrupted diffuse stellar substructure in the outer halo of M31 .
The core of the substructure lies at a projected distance of \sim 100 kpc from the centre of M31 in the outer halo , with possible extensions reaching right into the inner halo .
Using Pan-Andromeda Archaeological Survey photometry of red giant branch stars , we measure the distance , metallicity and brightness of the cloud .
Using Hubble Space Telescope data , we independently measure the distance and metallicity to the two globular clusters coincident with the East Cloud core , PA-57 and PA-58 , and find their distances to be consistent with the cloud .
Four further globular clusters coincident with the substructure extensions are identified as potentially associated .
Combining the analyses , we determine a distance to the cloud of 814 ^ { +20 } _ { -9 } kpc , a metallicity of [ Fe / H ] = -1.2 \pm 0.1 , and a brightness of M _ { V } = -10.7 \pm 0.4 mag .
Even allowing for the inclusion of the potential extensions , this accounts for less than 20 per cent of the progenitor luminosity implied by the luminosity-metallicity relation .
Using the updated techniques developed for this analysis , we also refine our estimates of the distance and brightness of the South-West Cloud , a separate substructure analyzed in the previous work in this series .