(CNN) -

After almost two years in captivity, Peter Theo Curtis is finally home.

The American writer flew Tuesday from Tel Aviv, Israel, to the United States -- stopping first in Newark, New Jersey, before reuniting with his mother in Boston, his family said in a news release.

"I have been so touched and moved, beyond all words, by the people who have come up to me today -- strangers on the airplane, the flight attendants and, most of all, my family to say welcome home," Curtis said.

The reunion meant an end to a dramatic ordeal for Curtis, who was held by Islamist rebels in Syria.

His mother, Nancy, said she was "overwhelmed with relief" now that he was back in the United States.

But, given the recent beheading of American journalist James Foley -- who was also being by militants in Syria -- she couldn't bring herself to celebrate.

"I don't think anybody's in the mood of celebration. You know, we're relieved," Nancy Curtis earlier told CNN outside her home in Cambridge, Massachusetts. "But after the events of the last week and knowing those other children of my friends are in danger, you know, I have very conflicted emotions. I've come to know the other families as well, and these kids have a lot in common."

In fact, the first person Nancy Curtis contacted after confirming that her son had been released was Foley's mother, Diane, she told "ABC World News Tonight."

Peter Theo Curtis, 45, is believed to have been captured in October 2012 and held by al-Nusra Front, a Syrian rebel group with ties to al-Qaida.

"You learn to get over the panic," Nancy Curtis told CNN's Anderson Cooper. "You learn to just take each hour as it comes."

Matt Wormser, a Vermont resident and Peter Theo Curtis' former high school roommate, said it was a "very bittersweet time" for friends and relatives of the freed hostage, given Foley's death.

"It's been tremendously difficult for Nancy," he said.

The United Nations said Peter Theo Curtis was handed over Sunday to U.N. peacekeepers in the Golan Heights, which is under Israeli government control, and was given a medical checkup.

State Department spokeswoman Marie Harf said Peter Theo Curtis was brought to Tel Aviv, to undergo some medical evaluations.

"He appears to be in good health," Harf added.

He briefly called his mother from Tel Aviv on Sunday, Nancy Curtis said.

"He said, 'Mom, they're just being so nice to me. They put me in this wonderful hotel, and I'm drinking a beer, and there are women out there,' " she recalled. "Because he's been in a cellar for two years, and he hasn't seen anything, no street life or obviously no women to be seen, and so he was really excited, and he was thrilled to be in Tel Aviv and frustrated that he can't go out because the place apparently is surrounded by paparazzi."

Nancy Curtis expressed gratitude to many for helping secure her son's release, including the FBI, Secretary of State John Kerry, Massachusetts Sen. Elizabeth Warren, Atlantic Media Chairman and owner David Bradley, U.N. Ambassador Samantha Power and, especially, the government of Qatar.

"Here's this extraordinary woman, and she said, 'We are going to get Theo free,' and after we made those contacts, things moved rapidly," Nancy Curtis said of Alia Al Thani, Qatar's permanent representative to the United Nations.

Qatar recently helped arrange the exchange of Sgt. Bowe Bergdahl, the only U.S. service member held by militants in Afghanistan, for five Taliban detainees held in the U.S. military base at Guantanamo Bay, Cuba.

The United States was not involved in negotiations for Peter Theo Curtis' release but was aware of private efforts to secure the release, two U.S. law enforcement officials said.

Harf, from the State Department, said Qatari officials "told the family very clearly that they did not pay ransom" -- something the United States government, as a policy, doesn't do when dealing with kidnappers and terrorists.

Peter Theo Curtis' release was announced just five days after ISIS militants released a video of one of its militants beheading Foley.

His mother said she thinks about other Americans being held in Syria.

"They have a good reason to be where they were," she said. "The journalists were there to bear witness and to interpret and to explain to people what's going on in the Middle East, and they have the experience to do that intelligently. And the other two were health workers. They were there to give meaning to their lives and make the world a better place. Those are all idealistic people."