The couple are said to be planning to exchange vows on 10 September at Babington House in Bath, according to The Mirror.
The 'Read All About It' rapper popped the question to the former reality star earlier this year but the couple have kept quiet about the date they will tie the knot.
Pro Green - whose real name is Stephen Manderson - is said to have asked his friend Lewis Richards to be best man.
Millie's pal Rosie Fortescue will be at the nuptials, but other than that it seems none of the 'Made In Chelsea' cast will be there.
The Quality Street heiress was first rumoured to be leaving the reality TV show in April over disagreements about filming her wedding preparations and the actual day.
A source has now told The Mirror: "This will be very much a day for Stephen and Millie and their friends, not part of a television show. Everything has been very low key, with their joint stag and hen do being a meal out in London and a private area in a hotel.
"Nothing has been over-the-top or 'celeby'. They want the same to be said of the wedding, so it's a tasteful, mid-week bash."