Los Angeles, California - Millie Bobby Brown has given fans a peek at her rarely-seen upper thigh tattoo.

The 21-year-old gave fans plenty of FOMO via her Instagram story on Monday, which shared another look at her beachside birthday trip.

In a clip set to Busy Woman by Sabrina Carpenter, Millie poses for the camera as he holds a sand bucket and a paper bag.

The Enola Holmes actor was rocking a glittering string bikini, revealing a glimpse of a small tattoo inked on her upper left thigh.

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The design is not quite able to be deciphered in the clip, but it appears to be a word or phrase written in cursive.

Millie's new ink joins an increasingly extensive collection of tats, most of which are similarly small.

So far, she's shown off a butterfly on her right hip, a heart on her collarbone, her grandmother's name on her ribcage, a cowboy hat on her right arm, and a rose on her back.

Millie also has "011" inked on her wrist to match the number her Stranger Things character, Eleven, has stamped on her wrist.

Earlier this month, she revealed another new piece of ink – a small "JB" on her ankle to honor her husband, Jake Bongiovi.