"Happy 4yr anniversary baby!! I am so honored to be the mother of your babies and loved by you every moment," Jessica captioned a snap of her and Eric Johnson kissing.
The pair were celebrating the birthday of their close friend Tom Everhart, an American artist who is the only artist authorised to paint the Peanuts comic strip characters.
In a second post Jessica showed her nearly half a million followers a picture of her and Eric posing in front of a painting Tom had created of Snoopy, and captioned it: "I can't wait to marry you!!! Best 4yrs of my life!!! Thank you @tomeverhartstudio for being an amazing mentor to us all. Happy Birthday...again :)"
Jessica and Eric are parents to two adorable children, Maxwell and Ace, and have already postponed their wedding due to her pregnancies. But Jessica recently opened up on their wedding plans, revealing "It will definitely be extravagant. I don't do things small."
Speaking to Savannah Gutherie on The Today Show, Jessica also spoke about her hugely successful fashion empire, which is estimated to be worth £595million.
Explaining how the Jessica Simpson Collection has gone from strength to strength, the blonde beauty - who was previously married to Nick Lachey - said, "I think that I can relate to every woman out there. I have been every size there is, so I know how to dress every body type."
She also discussed being a Weight Watchers spokeswoman, for which Jessica has been proudly showing off her svelte figure in adverts for the brand.
She also admitted that she has never been happier, telling People magazine: "Knowing that I have the wedding coming up is an incentive to stay on Weight Watchers, count my points and stay in the gym.
"I mean, when you see my dress, you'll know."