Jenelle Evans, star of MTV's Teen Mom 2, celebrated a very special birthday on Friday when her eldest son Jace turned five.

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Evans marked the occasion with a birthday message on Twitter which included side by side photos of an infant and five-year-old Jace. "happy birthday Jace!!!" she wrote, "5 years went by super fast. Cherish every moment and always be there for yr child".

The MTV family marked the occasion with a visit to the aquarium on Saturday, where Evans remarked that her son got to see "real mermaids" and run around with his young cousin.

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Early Sunday morning Evans returned to Twitter to boast some birthday fun. "Time to start preparing for little man's birthday party today," she tweeted, followed by a small cartoon balloon.

While Jace's birth father Andrew Lewis appears to have been absent from the scene, Jace enjoyed celebrating his birthday with his mom, newborn brother Kaiser, and Kaiser's father Nathan Griffith.

Evans has been taking special steps throughout July to assure Jace that he has not been replaced by little Kaiser, including "one-on-one" time hanging at the beach or making silly faces for the camera. As shown in early videos from when Jace was only six-months-old (featured below), making faces and snuggling has long been a favorite past-time for the MTV star and her little boy.

Teen Mom 2 continues on MTV with new episodes Wednesdays at 10 p.m. ET/PT.

Tags: Teen Mom 2 MTV Reality TV