  We study the exclusive photoproduction of a lepton pair off the proton with
the aim of studying the proton quark structure via the Generalized Parton
Distributions (GPD) formalism. After deriving the amplitudes of the processes
contributing to the $\gamma P\to P' e^+e^-$, the Timelike Compton Scattering
and the Bethe-Heitler process, we calculate all unpolarized, single- and
double- beam-target spin observables in the valence region in terms of GPDs.
