When the train stopped at the Bedford Ave. station in Williamsburg, the argument spilled out of the train and onto the platform, cops said. Beauchamp attacked Basin and the two fell onto the tracks as a Manhattan-bound train rolled into the station, cops said.



Beauchamp scampered out of the track bed and took off, but Basin — a junior student at LaGuardia Community College — was hit by the train as he struggled to get back on the platform, police said.



Basin died a short time later at Bellevue Hospital.



Beauchamp was caught on surveillance video leaving the subway station after the brawl. Cops later matched the images to a mugshot taken of Beauchamp after an arrest for being in Central Park after hours on Oct. 8, sources said.



Beauchamp — who attended The Hill School in Pottstown, Pa., in the 1990s with Donald Trump Jr. — showed signs of mental illness as a teenager, sources and a friend said.



“He always struggled academically, but everybody liked him,” said one childhood friend, who declined to use his name. “But he was just kind of an odd bird ... He’s kind of gotten crazy over the years and I just kind of ignored him.”



A wake will be held for Basin at James Romanelli Funeral Home in Ozone Park, Queens, on Wednesday between 2 p.m. and 9 p.m.



His funeral will be at St. Helen’s Roman Catholic Church on 83rd St. in Howard Beach at 10:40 a.m. Thursday.



With Sarah Armaghan



jkemp@nydailynews.com