Lady Gaga Brazil Concert Bomb Plot Suspect Was Deported From U.S. in April, Investigators Say

The man allegedly behind the planned bombing of Lady Gaga's recent concert in Brazil was deported from the United States just last month ... this according to Brazilian investigators.

Luis da Silva and a 17-year-old male were arrested hours before the massive free concert on Copacabana Beach in Rio, which brought out more than 2.5 million fans Saturday to cheer her on. Cops allege the two suspects planned to blow up bombs near the stage and execute fans, including children, at the show.

The New York Post reports authorities are now saying da Silva was kicked out of the United States in April ... however, they're still looking into the reason for the deportation.

As we told you ... the two were arrested after investigators say they tried to use social media to radicalize teenagers, encouraging them to use Molotov cocktails and other explosives at the show.

Officials say they carried out raids at multiple locations on the day of the concert ... keeping things quiet so people didn't panic.

They played it so close to the vest, in fact, that Gaga's team told us they learned about the alleged plot the day after from media reports ... cops never said anything.