Reports said the victim, Arthur Almendras, had just arrived at his farm in Barangay Darong on board a jeepney when two men shot him with caliber .45 pistols, killing him on the spot.
The elder Almendras was considered one of the leading politicians in the South in the 1960s.
His children were known to be locked in a bitter dispute over the familys lands in Davao del Sur.
Police, however, refused to say if Arthurs killing had anything to do with the land dispute.
Arthurs younger brother Alexis used to be a Davao City councilor, while another sibling, Al, once served as provincial board member of Davao del Sur.