Mills, who dashed back from Isle Of Wight where Pro Green was performing yesterday to be by his side today, beamed with pride for the successful star.
The MIC star looked cool in jeans, Hunter boots, a sheepskin jacket and a hat as she looked on.
She tweeted: "Round 2! @bbcr1 #hackneyweekend let's go!" and then posted a picture of herself backstage.
And she revealed she'd met her ultimate girl crush Lana Del Rey, who is also performing today.
She posted: "Just met lana del ray!!! Wow! She is my dream girl! #hackneyweekend"
And her boyfriend also raved about meeting the American. He posted: "Met @LanaDelRey as I was leaving, absolute sweetheart."
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But there's no rest for the wicked as Millie Mack revealed she's flying off to Majorca next.
It's usually Pro Green who takes on the proud role in the relationship so today saw a bit of a role reversal.
We spied him looking seriously chuffed as Millie made it onto the FHM Sexiest Women list earlier this year.
But today is all about his music - after he returned to home roots Hackney to hit the stage along with the likes of Jessie, Plan B and Rihanna.