Jake Paul stripped all the way down to his birthday suit for his 25th cake day on Monday ... going buck naked for a sexy photo with his model girlfriend.
The Problem Child just posted the spicy pic to his social media page ... showcasin' his naked bod while a bikini-clad Julia Rose did just enough to cover up his junk.
Jake rocked a hat and some expensive jewelry -- and not a thing more -- while Rose had her hands draped all over him.
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Jake captioned the photo with some of his goals for his next calendar year -- one of which included "go to outer space with Jeff, Richard, or Elon."
The b-day love for the YouTuber-turned-boxing superstar, meanwhile, has poured in all day ... with Rose writing on her social media page, "happy birthday dubba dubba…I can’t wait to feed you popcorn and kiss your nose until you turn 80."