A homeless sex offender was arrested over the weekend in the brutal sexual assault of a 19-year-old woman about a block from Gracie Mansion, police said.

Quincy Burks, 30, was again hanging around the Upper East Side on Monday when detectives investigating the sexual assault from a few days ago discovered and arrested him, police sources said.

According to a criminal complaint, he was accused of attempted rape and sexual abuse.

The disturbing attack occurred around 1:15 a.m. Saturday near East 90th Street and East End Avenue, about a block from the mayor’s office.

According to police and Manhattan Assistant District Attorney Katelyn Colman, the teenage victim was walking when Burks – who was captured on surveillance camera footage following her from Carl Schurz Park – threw her to the ground and then attacked her.

“The defendant is accused of brutally sexually assaulting a stranger on the sidewalk of the Upper East Side,” Colman said Tuesday at his arraignment in Manhattan Criminal Court.

Burks, who had been holding the victim’s hands, put his hand over her mouth when she began to scream, according to Colman.

The madman was frightened when a heroic doorman rushed to the woman’s aid after hearing her cries for help, police reported.

“This young lady was lying on the floor, crying desperately, with blood on her shirt and nose,” recalled bouncer Hector Mateo.

Mateo, who stayed with the victim until police arrived, said he has a 20-year-old daughter and his “fatherly instincts took over. I just wanted to help.”

He doesn’t normally work nights, but his wife told him, “This was basically God’s will to put me in the right place to help someone else.”

The victim’s condition was stable and he was taken to New York Presbyterian Cornell Medical Center, police said.

Her alleged attacker – who had only lived in the city for a few months – made his way a few blocks north to a public storage facility, where he accessed his storage locker and changed clothes, Colman said.

Several hours after the attack, police released surveillance footage showing the slim, bearded man wearing a white shirt and carrying a black umbrella, leisurely walking along the sidewalk.

In another clip, what appears to be the same person – this time wearing a black shirt – can be seen sprinting across a crosswalk.

In a third video, the man – previously described by police as being 6 feet tall – stopped on the sidewalk to check his phone and looked suspiciously over his shoulder several times before walking away.

Burks’ attorney Brett Taylor argued that police “may have arrested the wrong person” because his client, whom he described as a part-time delivery driver from Brooklyn, was not seen in the “incident itself” on surveillance videos.

He pushed for supervised release, but Judge Pamela A. Goldsmith granted prosecutors’ request to hold Burks without bail.

According to police, Burks has never been arrested in the Big Apple before.

But Goldsmith said he has a “very long record” in Detroit for assault and battery with a dangerous weapon.

These arrests occurred in 2018 and 2022, but it is unclear whether he was ever actually convicted.

Burks is scheduled to appear in court again on Friday.