The biological mother of accused Florida State University shooter Phoenix Ikner kidnapped him and fled to Norway amid a bitter custody battle a decade before the deadly shooting, court documents reveal.

Anne-Mari Eriksen took her then-11-year-old son to the Scandinavian nation in March 2015 in violation of the custody agreement she had with Christopher Ikner — after telling the father she was taking him to South Florida for spring break, according to a probable cause affidavit from the Leon County Sheriff’s Office viewed by The Post.

Eriksen and Phoenix Ikner — who at the time went by his birth name, Christian Gunnar Eriksen — both have American and Norwegian citizenship.

“Instead of staying in South Florida, the defendant allegedly fled the country with him in violation of their custody agreement,” the affidavit stated.

Christopher Ikner only discovered his son had been kidnapped when the 11-year-old spilled the beans during a phone call with his dad.

Eriksen — who had custody rights, though the agreement stipulated that she could not take him from the country without advance notification — said she would return the boy to the US and his dad on March 27, but failed to do so, according to the affidavit.

Christopher Ikner then quickly became worried and alerted authorities, saying his son “has developmental delays and special needs,” which he feared would not be taken care of without access to his regular doctors.

The affidavit said Phoenix Ikner was “on medication for several health and mental issues, to include a growth hormone disorder and ADHD.”

The mom didn’t return to the US until July 27, 2015, when she was arrested at Fort Lauderdale-Hollywood International Airport. She later pleaded no contest to illegally removing a child from Florida.

Months later, in October 2015, Eriksen filed a lawsuit alleging slander and libel against Christopher Ikner, his wife, Jessica Ikner, as well as two other relatives.

“The emotional and psychological harm done to the minor child will be evident for years, and will require counseling, and given the child being the age of 11, will have memory impacted by the behaviors of all the defendants for the false claims done on his mother, and for the parental alienation of the close relationship
of the minor child,” the suit stated.

Eriksen sought $80,000 in damages to use toward the boy’s college fund.

Phoenix Ikner was also listed as a plaintiff in the suit, which was dismissed seven months later.

Christian Gunnar Eriksen changed his name to Phoenix Ikner in 2020.

The now-20-year-old is accused of opening fire on the Tallahassee campus, killing two people and wounding five others, on Thursday afternoon.

The deadly rampage began near the campus’s student union building.

Terrifying video captured the moment a gunman walked through the area, firing shots from a handgun believed to be the old service weapon owned by his stepmom, Jessica Ikner.

Heavily armed first responders converged on the area and confronted the gunman.

Officials say Ikner didn’t comply with commands and was shot before being taken into police custody.

He was hospitalized for his injuries.

Before the suspected gunman’s identity was revealed to the public, Eriksen ranted against Christopher and Jessica Ikner for failing to communicate with her regarding her son’s whereabouts.

“Horrible when your alienating son’s dad is as mentally unstable as he is, along with his LCSO cop wife, that they can’t respond when you write to ask if everything is alright with my son, who studies at FSU,” Eriksen wrote in a now-deleted Facebook post viewed by the Daily Mail.

“That whole familly [sic] is nuts. He should write a book on how to parent badly, but he can’t communicate,” Eriksen added.

“Feel sorry for everyone at FSU and their kids.”

The two fatal victims, whose names weren’t revealed, were not students at the school, chief of campus police Jason Trumbower said.

Officials have not revealed a motive behind the attack.