The teenage son of fallen NYPD police officer Rafael Ramos -- one of two officers fatally shot in Brooklyn Saturday -- has paid tribute to his father on social media.

On his Facebook page, Ramos' 13-year-old son Jaden, wrote in heart-wrenching language about the loss of his father, calling it "the worst day of my life."

The middle school student said his father was always there for him. "He was the best father I could ask for. It's horrible that someone gets shot dead just for being a police officer. Everyone says they hate cops but they are the people that they call for help. I will always love you and I will never forget you. RIP Dad."

In a Dec. 9 post -- days before Rafael Ramos, of Brooklyn, turned 40 -- Jaden posted a photo collage of his father alone and with various family members and wrote: "Happy birthday to the best dad in the world, you are always there for me even when it's almost impossible. We have so many good times it's not even funny, I love you so much."

Jaden ribbed his dad a bit on hitting the big 4-0. "How does it feel to be 40? Your [sic] getting old dad but you still look good. Hope you have the best birthday, you deserve it."

Rafael Ramos and his partner Wen Jian Liu, 32, were shot execution-style at point-blank range in the ambush attack near the intersection of Myrtle and Tompkins avenues in Bedford-Stuyvesant at 2:47 p.m., police said.

The killings happened just as the NYPD received word from police in Baltimore County, Maryland, that the gunman, Ismaaiyl Brinsley, 28, had shot his former girlfriend and might be on his way to New York to harm police.