  We report on a 63-ks long XMM-Newton observation of the accreting millisecond
pulsar SAX J1808.4-3658 during the latest X-ray outburst which started on
September 21st 2008. The pn spectrum shows a highly significant emission line
in the energy band where the iron K-alpha line is expected, and which we
identify as emission from neutral (or mildly ionized) iron. The line profile
appears to be quite broad (more than 1 keV FWHM) and asymmetric; the most
probable explanation for this profile is Doppler and relativistic broadening
from the inner accretion disc. From a fit with a diskline profile we find an
inner radius of the disc of 8.7^(+3.7)_(-2.7) R_g, corresponding to
18.0^(+7.6)_(-5.6) km for a 1.4 Msun neutron star. The disc therefore appears
truncated inside the corotation radius (31 km for SAX J1808.4-3658) in
agreement with the fact that the source was still showing pulsations during the
XMM-Newton observation.
