WASHINGTON -- Jon Hammar, the Marine veteran from South Florida detained for months in a Mexican border prison for bringing his great-grandfather’s shotgun into the country, is expected to be released Friday in what his mother calls a “Christmas miracle.’’

His mother, Olivia, said she and her husband were awoken by a 2:30 a.m. phone call from Hammar’s defense attorney sharing the good news. Hammar’s father, Jon, quickly found a flight to Texas.

“We made it from our house in Palmetto Bay to the airport in 11 minutes,” she told The Miami Herald. “This is our Christmas miracle.”

The elder Hammar will wait for his son, who has been held since August in a prison in Matamoros, Mexico, across the border in Brownsville, Texas. They will likely remain there for a few days, Olivia Hammar said, because her son is interested in getting back the 1972 Winnebago motor home — and some nine surfboards he was transporting — from Mexican authorities.

“It will be closure for him,” she said.

Hammar was arrested Aug. 13 when he and a fellow Marine veteran, who were headed to Costa Rica to surf ,tried to cross into Mexico. Hammar had been told by U.S. authorities he could declare a six-decades-old .410 bore Sears & Roebuck shotgun at the border. The firearm is suitable for shooting rabbits and birds.

But Mexican authorities dismissed Hammar’s U.S. registration papers for the disassembled relic. Prosecutors charged him with a serious crime: possession of a weapon restricted for use to Mexico’s armed forces.

Hammar was sent to the Matamoros prison, where, at one point, inmates affiliated with local drug cartels called Hammar’s parents to try to extort money from them.

U.S. officials intervened, and Hammar was separated from the general inmate population but still spent much of his time chained to a bed to keep him from fleeing.

McClatchy, The Herald’s parent company, first reported on Hammar’s plight Dec. 6, when his family decided to go public with the case. Lawmakers responded quickly. Sen. Bill Nelson, a Florida Democrat, exhorted Mexico to release Hammar. Rep. Ileana Ros-Lehtinen, a Miami Republican and the family’s congresswoman, used her position as chairwoman of the House Foreign Affairs Committee to put pressure on U.S. and Mexican authorities.

She lashed out at the Obama administration for what she said was a failure to offer details on efforts to free Hammar and persuaded scores of her congressional colleagues to sign letters to the State Department and the Department of Homeland Security on Hammar’s behalf.

Ros-Lehtinen took to Twitter on Friday morning to publicize Hammar’s imminent release after his mother called the congresswoman’s Washington office.

“We couldn’t believe it, but prayers and hard work really paid off,” Ros-Lehtinen said. “It looks like we will have him home for Christmas.”

Nelson, whose office also spoke to Hammar’s mother, said an aide to a legal representative of the Mexican attorney general’s office confirmed the pending release. The U.S. Consulate is standing by to escort Hammar back to the United States.

“No American should be in a Mexican jail for five months without being able to have his case in front of a judge,” Nelson said. “We’re grateful; this is a good Christmas present.”