A Brooklyn man shot in the head by his retired cop neighbor earlier this week has died, police said Friday.

Joseph Stepinski, 45, died at Bellevue Hospital, four days after ex-cop Gene Barrett shot him in broad daylight in front of their shared rowhouse on Greenpoint Ave. in Greenpoint, police said.

Stepinski, was Barrett's superintendent's boyfriend, and the two men had a long simmering feud, police said. Barrett, 51, who retired from the NYPD on disability in 2002, was arrested Monday afternoon after a standoff.

Prosecutors are expected to upgrade the charges against him to murder.