The Danity Kane singer, who turns 30 on Tuesday, celebrated a couple days early with a bash at Bootsy Bellows in Hollywood on Saturday night.
Stepping out in a very low-cut sequined cocktail dress, O'Day looked sexy in her mermaid-inspired get-up.
"Celebrating the start of turning 30!#MermaidRealness," she posted on Instagram before going out for the night -- sharing a profile shot of her bod that is sure to inspire envy.
Aubrey and the rest of the Danity Kane girls are hard at work on brand new music, following their "comeback" concert in December.
"We really want to be able to go from, you know, touch Shannon's country roots, touch Andrea's Latin roots, touch R&B, touch pop, touch rock, but always continue our urban pop sound vocally with the blend of our voices," O'Day recently told MTV News about their upcoming songs.
Are you excited to see more from DK ... or should they stay in the '00s?
See more of your favorite "TRL"-era pop stars Then & Now in the gallery above!