A Brooklyn man stabbed his 80-year-old grandfather to death in the senior’s Long Island home late Monday, authorities said. 

John Pilgrim, 80, was inside his home on Hounslow Road near Clyde Road in Shirley around 7:45 p.m. when his grandson, Christopher Clarke, 34, carried out the deadly assault and fled, Suffolk County Police said. 

Clarke, of Park Slope, was tracked down about two hours later to the Long Island Railroad Station in Shirley, cops said.

He was arrested and charged with second-degree murder, authorities said. 

He is being held at the Sixth Precinct and is scheduled to be arraigned in First District Court in Central Islip Tuesday. 

The circumstances leading up to the fatal stabbing were not immediately clear.