Russell Brand In Custody -- Citizen's Arrest

Russell Brand has just been arrested for allegedly attacking paparazzi at LAX airport ... TMZ has learned, and it was a citizen's arrest.

of another angle of the incident.

UPDATE 5:54 PM PT: Russell has posted $20,000 bail and has left the police station.

Around the same time, Katy defended Russell via Twitter, saying, "If you cross the line & try an put a lens up my dress, my fiancé will do his job & protect me."

The alleged upskirting is not seen in video of the incident.