Context : The high-mass microquasar Cyg X-1 , the best-established candidate for a stellar-mass black hole in the Galaxy , has been detected in a flaring state at very high energies ( VHE ) , E > 200 GeV , by the Atmospheric Cherenkov Telescope MAGIC .
The flare occurred at orbital phase \phi = 0.91 , where \phi = 1 is the configuration with the black hole behind the companion high-mass star , when the absorption of gamma-ray photons by photon-photon annihilation with the stellar field is expected to be highest .

Aims : We aim to set up a model for the high-energy emission and absorption in Cyg X-1 that can explain the nature of the observed gamma-ray flare .

Methods : We study the gamma-ray opacity due to pair creation along the whole orbit , and for different locations of the emitter .
Then we consider a possible mechanism for the production of the VHE emission .

Results : We present detailed calculations of the gamma-ray opacity and infer from these calculations the distance from the black hole where the emitting region was located .
We suggest that the flare was the result of a jet-clump interaction where the decay products of inelastic p - p collisions dominate the VHE outcome .

Conclusions : We are able to reproduce the spectrum of Cyg X-1 during the observed flare under reasonable assumptions .
The flare may be the first event of jet-cloud interaction ever detected at such high energies .