The blonde beauty got to know the portrait artist in 2002 when she agreed to pose nude for him while pregnant with her daughter Lila Grace.
Moss was fascinated to learn Freud tattooed sailors during his stint in the Merchant Navy during World War II, and was thrilled when he offered to etch two tiny swallows on her back.
She recalls, ""He told me about when he was in the Navy, when he was 19 or something, and he used to do all of the tattoos for the sailors. And I said, 'Oh my God, that's amazing.' And he went, 'I can do you one. What would you like? Would you like creatures of the animal kingdom?' I said I liked birds and he replied, 'I've done birds. I've got it in my book.' And he pointed down at a painting of a chicken upside down in a bucket. And I said, 'No, I'm not having that.' And then he said, 'Maybe I should just do you.' And I thought, I'm not going to have a girl on my a**e. So we decided to do a flock of birds.""
Moss is convinced the designs at the base of her spine are priceless, telling Vanity Fair, ""I mean, it's an original Freud. I wonder how much a collector would pay for that? A few million? If it all goes horribly wrong I could get a skin graft and sell it. It's probably the only one on skin that's still around, because when he was in the Navy he was about 19. Can you imagine?""
Moss also has an anchor tattoo on her wrist as well as a heart and star design.
Freud's painting of Moss showing off her baby bump while reclining naked sold for $6.2 million (£3.9 million) at auction in 2005.