The 'Read All About It' hitmaker popped the question to the reality TV star in Paris on Monday night (25.03.13) and has now revealed he chose the diamond for the 'Made in Chelsea' beauty's dazzling band.
But the rapper - whose real name is Stephen Manderson - joked it was a ''bit selfish'' of him to create the eye-catching jewellery, which is just under three carats and made up of a large rock set on fashionable double bands encrusted with diamonds.
He told the Daily Mirror newspaper: ''I chose the diamond, then I designed the whole thing around it. I had to just hope she liked it, too. A bit selfish of me, really.''
Millie was spotted admiring her sparkling new band on the streets of Paris shortly after accepting Pro Green's proposal, and just hours later the couple partied arm-in-arm in London on Tuesday night (26.03.13), where the 23-year-old beauty said the rapper had picked the ''perfect ring''.
She told MailOnline: ''He's picked the perfect ring, it's really classy and just me.
''It's a radiant setting, it's so sparkly and it's big but too big to wear every day.''
Millie insists the pair - who started dating in December 2011 - are yet to make any plans for their nuptials and she is looking forward to ''enjoying'' her engagement.
When asked when the wedding would take place, she replied: ''I'm not putting any pressure on it. I'm not thinking about that right now, I'm just going to enjoy being engaged.''
Following Green's proposal on Monday, Millie took to her Twitter account to announce the news by posting a picture of her sparkler.
In a message accompanying the image, she wrote: ''If I could scream loud enough for the whole world to hear I would.''