Boxing trainer Brian 'Bomac' McIntyre has been charged with possession of a firearm after a gun was found in luggage at Manchester Airport.
McIntyre, 53 trained Chris Eubank Jr for the Briton's rematch with Liam Smith on Saturday.
He was arrested at the airport on Sunday as he prepared to board a flight back to the United States.
McIntyre was remanded in custody by magistrates on Monday and is due appear at Manchester Crown Court next month.
"Officers were called to reports of a possible firearm being found in hold luggage by airport staff at Manchester Airport," Greater Manchester Police (GMP) said.
"GMP officers attended, and the firearm was seized.
"Subsequently, a 53-year-old man was arrested for possession of a firearm and was taken to custody for further questioning.
"Brian McIntyre from the United States of America was charged with possession of a firearm and possession of ammunition for a firearm without a certificate."
McIntyre was remanded into custody after attending Stockport Magistrates Court on Monday.
He is next due to appear at Manchester Crown Court on Monday, 9 October, police said.
The incident took place at about 10:45 BST on Sunday as McIntyre was preparing to board a flight back to the US following 33-year-old Eubank's 10th-round TKO victory against Smith at Manchester Arena.
American McIntyre is widely regarded to be one of the best boxing coaches in the world and is responsible for guiding Terence Crawford to greatness - helping his countryman become the first two-weight undisputed world champion in the four belt era when he beat Errol Spence Jr.
McIntyre is firmly in the running to be named 'Trainer of the Year' for 2023.
Eubank's camp offered no comment when approached by BBC Sport.