In a pair of a heart-wrenching Facebook posts, the son of one of the two NYPD officers killed in Saturday's apparent ambush paid tribute to his slain father.

"This is the worst day of my life," Jaden Ramos, the 13-year-old son of Rafael Ramos, wrote.

"Today I had to say bye to my father," Jaden continued. "He was their [sic] for me everyday of my life, 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."

Jaden Ramos mourns his slain father. (Facebook)

Jaden's Facebook posts have been shared more than 8,000 times.

Police say Rafael Ramos, 40, and his partner, 32-year-old Wenjian Liu, were killed Saturday as they sat in their patrol car in Brooklyn by a gunman who earlier in the day had announced on social media that he planned to kill two "pigs" in retribution for the recent U.S. police killings of two unarmed black men, Eric Garner and Michael Brown.

Authorities say the gunman, 28-year-old Ismaaiyl Abdullah Brinsley, shot and wounded his girlfriend in Baltimore before traveling to New York where he shot both officers. Brinsley fled the scene, ducking into a nearby subway station where he shot and killed himself.

Hours earlier, police say, Brinsley warned on Instagram that he would be "putting wings on pigs today."

According to New York City Police Commissioner William Bratton, the NYPD received a fax at 2:45 p.m. from Baltimore police alerting them of Brinsley's threat, but it came too late. Brinsley opened fire on Liu and Ramos at 2:47 p.m., Bratton said.

“Officer Liu and Officer Ramos never had the chance to draw their weapons," Bratton said. "They may actually have never seen their assailant, their murderer."

Earlier this month, Jaden Ramos posted a message on Facebook marking his father's 40th birthday.

"Happy birthday to the best dad in the world, you are always there for me even when it's almost impossible," Jaden wrote on Dec. 9, tagging his father in a family photo. "We have so many good times it's not even funny, I love you so much."