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Brad Pitt isn’t sure his relationship with adopted son Maddox is salvageable after the 18-year-old has gone off to college in South Korea.

The “Once Upon a Time in Hollywood” star is said to be incredibly sad at the idea his eldest child “hasn’t been receptive” to his mother Angelina Jolie’s efforts to mend their shattered relationship.

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“Maddox hasn’t been receptive,” a source told Us Weekly of Jolie’s attempts to reconcile her son with the “Ad Astra" star. “And for Brad, it’s a tremendous loss.”

Pitt, 55, and Maddox have maintained a schism in their bond since the two allegedly got into an altercation while the family was traveling on a private plane to Los Angeles in 2016. The “Ocean’s Eleven” star was investigated for child abuse in the incident but was cleared of any wrongdoing.

INCHEON, SOUTH KOREA - AUGUST 26: Maddox Jolie-Pitt is seen at the entrance ceremony for Yonsei University on August 26, 2019 in Incheon, South Korea. (Photo by Han Myung-Gu/GC Images,)

Maddox Jolie-Pitt is seen at the entrance ceremony for Yonsei University on August 26, 2019 in Incheon, South Korea. Angelina Jolie dropped him off at school and he recently revealed he's not sure if Brad Pitt will visit him there. (Getty)

The father-son duo continued to be estranged after Pitt and Jolie split in 2016. Still, Pitt hopes he can remedy his relationship with the former A-list couple’s other son, Pax Jolie-Pitt, 15.

“With Maddox overseas, Brad is also hopeful that Pax will also be interested in reconnecting without the influence of his older brother,” the insider added.

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In a video obtained by In Touch Weekly, last month, Maddox was asked whether Pitt would visit him in college at Yonsei University in Incheon, South Korea, and Maddox was diplomatic, if vague.

NEW YORK, NEW YORK - FEBRUARY 25: Angelina Jolie with children Knox Leon Jolie-Pitt, Vivienne Marcheline Jolie-Pitt, Pax Thien Jolie-Pitt, Shiloh Nouvel Jolie-Pitt, Zahara Marley Jolie-Pitt and Maddox Chivan Jolie-Pitt attend

Angelina Jolie with children Knox Leon Jolie-Pitt, Vivienne Marcheline Jolie-Pitt, Pax Thien Jolie-Pitt, Shiloh Nouvel Jolie-Pitt, Zahara Marley Jolie-Pitt and Maddox Chivan Jolie-Pitt attend "The Boy Who Harnessed The Wind" Special Screening at Crosby Street Hotel on Feb. 25, 2019 in New York City. (Getty)

“I don’t know about that [or] what’s happening,” he said.

When asked if his relationship with Pitt was "over," he replied, “Well, whatever happens, happens.”

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Pitt and Jolie also share children Zahara, 14, Shiloh, 13, Vivienne, 11 and Knox, 11.

Zahara accompanied Maddox and Jolie last Thursday at the premiere of “Maleficent: Mistress of Evil” in Japan.

(L-R) Zahara Marley Jolie-Pitt, Angelina Jolie and Maddox Jolie-Pitt attend the Japan premiere of 'Maleficent: Mistress of Evil' at Roppongi Hills arena on October 3, 2019 in Tokyo, Japan. (Photo by Jun Sato/WireImage)

(L-R) Zahara Marley Jolie-Pitt, Angelina Jolie and Maddox Jolie-Pitt attend the Japan premiere of 'Maleficent: Mistress of Evil' at Roppongi Hills arena on October 3, 2019 in Tokyo, Japan. (Photo by Jun Sato/WireImage)

Jolie raved about her son after sending him off to college, adding that she struggled to hold back tears as she was walking away from the freshman student.

“I'm so proud of him," she gushed. "I'm so excited, I feel like my world expands as their world expands. I learn so much from them, and I love this stage."

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"I also, just at some point, had the big [sun]glasses and the amount of times I turned and waved,” Jolie added. “I do know it was the one moment in my life I think I turned around six times before the airport just ... and he sweetly stayed and kept waving, knowing that I was going to keep turning around. You could feel he knew he couldn't leave."

Pitt and Jolie were married for two years and together for 12 years after becoming close while filming "Mr. & Mrs. Smith" in 2005.