Brian Austin Green is officially — or we should say finally — saying goodbye to a sentimental tattoo … one he got in honor of Vanessa Marcil before their 2003 breakup.

Sources familiar with the situation tell TMZ … Brian finally went through with the removal about 15 years after first trying to scrap it. We’re told he tried deleting it when he and Vanessa split, but never got it fully wiped because the tattoo removal place shut down.

Brian got the ink after she gave birth to their son Kassius back in 2002 — the piece was the kiddo’s name with Vanessa’s name shaded inside it.

Y’know what they say about name tats, though … the young couple called it quits the next year.

The tattoo’s remained faint on his arm since his past removal sessions, but he finally went in this month to finish the job. As for honoring Kass … Brian still has another tattoo of his baby photo on his bicep. Always good to have a backup!

FYI, Brian and Vanessa went through a lengthy custody battle over Kass … and he also sued her, claiming she owed him roughly $200K in unpaid loans, but it was dismissed due to the statute of limitations.

We’re told the nasty ending definitely motivated BAG to finish the ink removal.