Looking chic and sophisticated in monochrome, the former Glee actress walked the red carpet along with Hollywood legend Michelle Pfeiffer, who stars as Dianna's mother in Martin Scorsese's latest movie.
Dianna wore a chic black and white Osman crop top and skirt, along with sexy, striped heels and dark, vampish nails.
And her hair looked amazing, having been backcombed at the crown and pulled loosely back into a ponytail.
But it was the eye make-up that really got us going here in the Reveal office. We see classic nudes and smoky eye make-up on the red carpet all the time, so when someone opts for a splash of colour, we ALWAYS get a little bit excited.
Dianna, 27, chose purple to complement her hazel eyes – probably the most versatile and flattering eye make-up colour there is!
Purple is the total opposite to green and brown so if your eyes are either of these colours, purple makes them really stand out.
If, however, you have blue eyes, purple might not be quite as eye-popping, so choose a warmer shade like plum or soft lilac to create the same effect. For inspiration, check out some of our favourite shades below...
To re-create Dianna's look, smudge your chosen purple over your eyelids to just above the socketline, working it out into a winged shape with an eyeshadow brush.
Next, use a purple kohl pencil to line underneath your bottom lashes and around the waterline of your eyes, then grab a thin, eyeliner brush and apply the same eyeshadow underneath your bottom lashes to complete your look.
Finish with lashings of black mascara, nude, glossy lips and a big, Hollywood smile!
What do you think of Dianna's purple eye make-up look? Let us know below – our fave comment across the site each week wins £50!