Former Boston Celtics center and NBA all-time great Bill Russell apologized on Sunday for bringing a loaded gun to an airport.

“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," the basketball legend said in a prepared statement.

The 79-year-old Russell was arrested on Wednesday as he attempted to go through security at Sea-Tac Airport in Seattle, Washington. Agents found a .38-caliber Smith & Wesson pistol in his carry-on luggage. He was issued a citation by the TSA and the gun was confiscated. He was later released from custody by the police of the Port of Seattle.

The gun, police found out, was licensed; however, it had six rounds. Airline regulations allow the transport of guns, but they have to be unloaded and be stored in checked in luggage.

A very public rivalry with center Wilt Chamberlain colored much of his post-NBA years, but Russell's friendship with the former Los Angeles Laker came to light when he delivered the eulogy at the latter's funeral in 1999.

After his playing career with the Celtics, where he averaged 15.1 points and 22.5 rebounds over the span of 13 years, he went into coaching, first with Boston, where he was the playing coach, and then with Seattle and Sacramento.

He then went into seclusion for around a decade, after which he resurfaced with an autobiography titled "Russell's Rules" in 2001. In 1998, he was honored with the Presidential Medal of Freedom, the highest civilian decoration in the United States, by President Barack Obama in 2010.

Russell was travelling to Boston for a ceremony in his honor, where a statue of him will be unveiled. He was also given honoris causa degrees by Suffolk and Harvard, both in the Boston metropolitan area, and was inducted in the inaugural class of the FIBA Hall of Fame in 2007.