The 22-year-old, who is best known for starring in the latest series of Love Island, got freshly inked in London over the weekend.
Molly, 22, took to Instagram on Saturday and shared a short video clip of her and Zach heading to Debut Studios in London.
In the video, Molly could be seen going through the tattoo process, which included choosing the design and getting it tattooed on her wrists.
Zach could also be seen feeding Molly grapes as the artist is working on her designs, before getting a tattoo of his own.
The clip finished with Molly smiling at the camera as she showed off her new body art which featured Zach's star sign.
Captioning the post, she wrote: “SO! Me & Zac headed to @debutstudios and got some new tattoos by @alexlloydtattoo.
"I decided to get both mine and Zac's Zodiac signs on my wrist & a cute little butterfly on my thumb to start my finger tattoos! I couldn’t be happier!”
Fans at home were divided about the decision, with several saying it was a "big issue."
One person wrote: "Stupid idea and far too early."
"Nooooo girl. Don't be getting any boys star sign," a second penned.
A third said: “Hope you don’t regret it."
Others quickly rushed to her defence, and one said: "Some people acting like she had Zach tattooed across her forehead."
A second fan commented: "Why everyone care if she gets Zach's sign or not... tattoos are part of a persons story."
It comes after Molly squashed split rumours with Zach as they reunited on the NTAs red carpet.
The couple looked closer than ever outside The O2, as they walked the red carpet before attending the ceremony.
Molly and Zach met on this year's summer series of the ITV2 show.
While they didn't have an easy ride during their time in the villa, they seem to be going from strength to strength back in the UK.