And the starlet gave us a sneak peek of her outfit and make-up by snapping a quick Instagram picture before heading over to the event.
Giving us a glimpse of her evening attire, Rosie looked very glam in an elegant black halterneck dress featuring delicate lace detailing (FYI, it's from Rosie's own collection for Lipstick Boutique and retails at £75).
But the star of her look had to be her a-mazing bold orange-red lipstick. We love it!
The fashion blogger ditched her usual nude and pink shades in favour of the vibrant hue, which came courtesy of NARS Velvet Matte Lip Pencil in Red Square, £18.
Rosie's told us in the past how much she loves her NARS lippy and we can totally see why - it provides impressive pigmentation in a single swipe and the formula feels conditioning before drying down to a matte finish.
Plus it comes in a chunky jumbo crayon form, making it perfect for bright pout newbies as it's super-easy to apply. Win!
If you want to get the look on a budget, check out Maybelline Colour Drama Intense Velvet Lip Pencil in Fab Orange, £4.99 - the formula is pretty similar but it costs a fraction of the price.
Make like Rosie and keep your eye make-up minimal with a touch of brown shadow through your crease and fluttery, mascara-clad lashes. Gorgeous!
What do you think of Rosie's fave lipstick colour? Let us know by commenting below as the best comment across the site each week wins £50!
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