The Long Island man arrested in connection with the Gilgo Beach murders was a high school classmate of BIlly Baldwin, the actor shared on social media Friday morning.

“Woke up this morning to learn that the Gilgo Beach serial killer suspect was my high school classmate Rex Heuermann,” Baldwin, 60, tweeted shortly before 11 a.m..

“Berner High School…Massapequa, New York…Class of 1981,” the “Flatliners” star continued.

Heuermann, 59, was still living in Massapequa Park when he was taken into custody in Manhattan on Thursday night.

He is due in court later today.

Baldwin – the younger brother of “30 Rock” star Alec Baldwin, 65 – was born and raised in Massapequa.

All four of the “Baldwin brothers,” which also includes actors Daniel, 62, and Stephen, 57, graduated from Berner High, which is now a middle school.

The suburb is about a 20-minute drive from the Gilgo Beach area, where the bodies of four women were found in late 2010.

Other Berner High grads were quick to discuss Heuermann’s shocking arrest in a public alumni Facebook group on Friday.

“He used to leave me little love notes in my locker,” classmate Maureen Boyle Holpit wrote underneath a post announcing the development.

“Omg I hope he goes to hell,” Massapequa resident Barbara Gaulrapp-Cox added.