"X Factor" producers tried to pull the wool over your eyes last night -- because TMZ has learned Simon Cowell and Britney Spears' mansions on the show weren't their homes at all ... in fact, one actually belongs to MLB star Alex Rodriguez.

In case you missed last night's episode, groups of contestants were invited to perform at four different homes around the country -- each allegedly belonging to one of the show's four judges.

But it was ALL A LIE -- "Simon's" Miami pad actually belongs to A-Rod. The baseball star listed the home in August for $38,000,000, but it's still on the market. Simon's real house is in Beverly Hills.

It's unclear who really owns the Malibu home Britney appeared in last night, but one thing's for certain -- Britney does NOT own that Malibu home. Her real home is in Calabasas, many miles away.

As for the other two homes -- we can't say for SURE if they're bogus, but we're betting none of the judges wanted their real homes on public display.

Sorry to burst your celeb real estate bubble.