NBA legend Bill Russell apologized after he was arrested at Seattle-Tacoma International Airport on Wednesday for entering with a loaded gun, CNN reported.

"Before boarding my flight from Seattle to Boston, I had accidentally left a legal firearm in my bag. I apologize and truly regret the mistake," Russell said in a statement. 

Russell, 79, was arrested and issued a state citation for bring a weapon into a prohibited area of the airport according to Perry Cooper, spokesman for Port of Seattle Police Department.

He was released by authorities after his citation was issued. Russell had .38-caliber Smith & Wesson handgun on him, said Lisette Garcia, spokeswoman for the Transportation Security Administration (TSA).

Authorities discovered the handgun while his carry-on was being screened at a security checkpoint. 

"Firearms, ammunition, firearm parts and realistic replicas of firearms are always prohibited in carry-on baggage. However, these items can be transported in checked baggage provided the traveler declares them to the airline during the ticket counter check-in process," a TSA statement explained.

The TSA also said Russell could be fined up to $7,500 for bringing the gun.

Russell is best known for his outstanding basketball career with the Boston Celtics, winning 11 championships, and for becoming the NBA's first African-American head coach.

He is also known for his dedication to civil rights. Russell walked with Dr. Martin Luther King, Jr. and had been an outspoken advocate for equality. In 2011, he was awarded with the Presidential Medal of Freedom -- America's highest civilian honor.

On Thursday, a Texas man from a town called Gun Barrel City was caught with a loaded gun at LaGuardia Airport in New York City.

Douglas A. White, 61, was charged with criminal possession of a loaded firearm after authorities discovered his gun at a checkpoint. 

He was in custody on Friday and has not yet commented on the case.