Prince Harry drove to help a friend who was mugged while speaking to the royal on his mobile phone and gave a statement to police about the crime, it has emerged.
Hearing the robbery, the helicopter pilot realised pal Thomas van Straubenzee was in trouble and quickly drove to the crime scene in Battersea, south west London.
When he could not find Mr van Straubenzee he searched for him until his "intuition" took him to the local police station where his friend was reporting the mugging, a source said.
Mr van Straubenzee's BlackBerry mobile phone was taken during the street attack which happened on 30 November and a suspect was later arrested and bailed.
A Metropolitan Police spokesman said: "Police are investigating an allegation of personal robbery which occurred at approximately 20:30hrs on Wednesday, 30 November in Albert Bridge Road, SW11.
"A mobile phone was taken during the robbery. This allegation was taken seriously, as are all allegations of robbery.
"A man was arrested on Thursday, 1 December on suspicion of robbery and bailed to return in January 2012 pending further enquiries.
"Police from Wandsworth are investigating.
"The property has been recovered. (There were) no reports of any injuries."
A source confirmed that the 27-year-old Prince had given a witness statement to police.