black long sleeve mini dress Rihoas Square Neck Knitted for Women, / XL 044 *Step into the dress for easier wear Lucy Black Long Sleeve Mini

Square neckline with tie straps for a soft shoulder detail

A natural waist and A-line silhouette give the bodice a defined shape before the skirt falls into a long, fluid line

Pairing a budget-friendly dress from an online retailer like Lulus with an investment designer handbag will give your entire look a high-end feel

Plunged long sleeve mini dress with an iridescent trim detail in black in a premium sheer Linen TENCEL blend

The flirty frock was worked on with Jenners stylist Monica Rose, and the dress, which is rumored to have cost $9,000, conjured up throwback images of another It girl celebrating her 21st birthday back in 2002: Paris Hilton