AJ McLean is remembering Liam Payne as "a light" in his life following the singer's recent death ... looking back on their time together working on a new Netflix show.
The Backstreet Boys member addressed the late One Direction star's passing at LAX, where he shared how he and Liam became friends while working on "Building the Band," a music competition series where singers get a chance to build the next great pop group.
AJ says they just finished wrapping the TV show ... where he, Liam, Nicole Scherzinger and Kelly Rowland worked closely together over a 6-week period and had "a great time."
AJ, who has battled addiction throughout his career, noted he didn't see any warning signs while working with Liam ... but, admitted the 2 boybanders had "lots of similarities."
Though, the duo never discussed their respective sobriety journeys, AJ said he and Liam talked a lot about "life" ... praising the late pop singer as "very funny" and a "sweetheart."
He added ... "Addiction is a real thing. Fortunately I came out the other end, but I’m one of few."
Right now, AJ is thinking about Liam's former bandmates, Harry Styles, Louis Tomlinson, Niall Horan, and Zayn Malik ... explaining how boyband members "become family" while working together.
As TMZ previously reported, Liam fell to his death from a third-floor balcony at the CasaSur Palermo Hotel in Buenos Aires, Argentina Wednesday. The singer had been in the South American country to support Niall's show at the Movistar Arena earlier in the month ... ultimately extending his trip to spend more time in Argentina's capital.
Police officials have said Liam jumped from his hotel balcony ... citing drugs as the likely cause of his erratic behavior last week. Liam's initial results from the autopsy have already come in ... with a toxicology report stating the singer had cocaine, crack, "Cristal" -- the Argentinian version of methamphetamine -- and other drugs in his body.
As we reported, Liam had been telling people he was sober earlier this year.