(CNN) -- For a while there, Kathy Amaya thought her long-lost son was gone forever.
He was 2 years old when her estranged husband took the boy to San Luis Potosi, Mexico, to visit grandparents.
That was 35 years ago, and that was the last time Amaya, now 60, saw her son.
Then, the U.S. Border Patrol called her this month and said a man who spoke only Spanish was claiming to be a U.S. citizen -- and that she was his mother.
At long last, the day that Amaya thought would never come finally arrived.
"We didn't talk over the phone, but I heard him" in the background during the call with the Border Patrol, Amaya said. "He was right there. I was asking his birth date and what town he is from because I wanted to know if it was the same."
Through a Border Patrol agent in California, the man answered the questions correctly. He was her son. Moreover, the Border Patrol agent earlier had researched the man's birth certificate and used that document to track down Amaya in Wisconsin: "All he told me was, 'You're really hard to track down, you know that?'" she said of the agent's phone call.
Hearing her son's voice for the first time in 35 years -- though it was in the background -- was "very emotional," Amaya said.
"After I got off the phone with the Border Patrol, I just sat down and cried for hours," Amaya said Wednesday.
Amaya had spent years searching for her son on the Internet and on Facebook. But now she knows why she couldn't find him: He was using her maiden name as part of his full name, David Amaya Barrick.
"It never dawned on me that he was using my maiden name," Amaya said.
Her son, who's now staying in the care of a San Diego church, couldn't be reached for comment Wednesday. Amaya said she is planning to travel from her Wisconsin home to San Diego to see her son in person on November 24.
The Border Patrol described the tale as "an unusual human story based on good investigative work and genuine compassion," the agency said in a statement.
Agents encountered the son in a canyon near Imperial Beach, California, and determined that he had crossed the border illegally with several other persons. They were all arrested, the Border Patrol said.
The son first said he was a Mexican citizen, but then claimed to be a U.S. citizen taken to Mexico by his father 35 years ago at age 2, the patrol said.
While traveling north through Mexico, bandits took David Amaya's cell phone and money, the Border Patrol said.
In checking his claim of being a U.S. citizen, agents called the Cook County vital records office in Chicago and received a fax of the birth certificate, the Border Patrol said.
After researching several sources, agents found the mother on November 1.
"Too often our Border Patrol Agents deal with the darker aspects of border security -- violence, drugs, and smuggling," Imperial Beach Border Patrol Agent-in-charge Gregory Bovino said in a statement. "But David's case was a welcome respite for all involved. It was truly inspirational to witness David talking with his mother for the first time."
The Border Patrol station is now raising funds for the son's trip back home.
The separation of mother and son began when the estranged husband took the boy from the care of his mother's sister on what seemed like a routine outing, Amaya said.
The family was living in Chicago near Midway Airport, and when the boy wasn't returned home promptly, the estranged husband told Amaya that he had taken the boy to Mexico for a month-long visit.
But the month became a year, and a year became decades.
"I was very upset. I begged him to bring him back," she said of her estranged husband, whom she eventually divorced in 1986.
The grandparents raised the boy because the father returned to Chicago and saw his son only a few times in the 35 years, Amaya said.
She went to police, but because the couple didn't settle on custody during the divorce, the police couldn't help her, she said. "Neither one of us had custody," she said.
Years passed. "I was very emotional for a while. I was upset and angry," she said.
Amaya went on to have four other children -- three boys and a girl -- and moved to Rice Lake, Wisconsin, in 1986. She moved to Chippewa Falls, Wisconsin, in 1999, where she lives now with two of her children, both in their 20s.
Now that she knows her son's whereabouts, they have been exchanging chat messages on Facebook, with a San Diego church pastor helping translate David Amaya's messages into English and then translating the mother's responses into Spanish, the mother said.
"David told me he was looking for me for a long time, and he couldn't find me," Kathy Amaya said.
The last time she saw her son, he spoke only a few words in English. "He wasn't speaking a whole lot back then. Just some words here and there. It was like 'mom' and 'dad' and 'play' and stuff like that," the mother said.
She found additional confirmation that the man was her son when she saw that her ex-husband is among her son's friends on Facebook.
She and her ex-husband have not spoken to each other in many years, she said. And she has no plans to ever speak to him again.
When she saw a photo of her son for the first time in 35 years on his Facebook page, she said: "Well, the first thing I thought of was he kind of resembled me a little bit, and he kind of resembles one of his brothers."
Her son holds no hard feelings about any unsuccessful family searches for him.
"I told him I was looking for him, and he told me that he was looking for me, and I told him I was sorry that I missed a lot in his life, and he told me we have a future to catch up," Kathy Amaya said.
Somehow, they will find a way past the language barrier once they see each other face to face for the first time in 35 years later this month. She doesn't know much about her son other than he played drums in a band in Mexico, even going on tour there. He wants a career in music.
Kathy Amaya, who works as an assistant housekeeper at a hotel, will bring her fiance with her on the flight to California this month.
When she flies to San Diego, it will mark another first in her life: She's never flown.
"I'm 60, and I've never been on a plane," she said. "I'm very old school."
Her son will then fly back with her to Wisconsin on November 26, reunited at last.
CNN's Casey Wian contributed from San Diego.