Tom Sandoval, Raquel Leviss Had Code Names For Each Other On Their Cell Phones

Tom Sandoval and Raquel Leviss went to great lengths to keep their affair out of Ariana Madix's sight, even creating fake names for each other on their phones, TMZ has learned ... despite Tom claiming she knew the warning signs.

Sources connected to the trio tell TMZ ... it was Tom's idea to create the code names, and Raquel was more than happy to go along.

They both picked basic names for each other -- he put the name "Jamie" in his phone. We don't know what alias she used for him.

Peeps close to Tom and Raquel shockingly knew about the fake names ... Tom even called Raquel "Jamie" to his friends on occasion. Not a smart move.

Ariana never cracked the code during their secret romance, but we're told she knows now.

Tom recently made an appearance on Howie Mandel's podcast ... claiming his affair was visible to Ariana, but she chose to turn a blind eye instead.