The professional dancer, who quit the BBC1 show this year, shared the good news with her fans and friends on Twitter yesterday (29 December).
Posting a beautiful shot from their grand location at St Pancras Renaissance, a luxury hotel in central London, Flavia wrote the message: "Had the most amazing day with family & friends @StPancrasRen xxx."
The picture shows Italian-born Flavia in an elegant white dress, while Coronation Street actor Jimi looks pleased as punch behind her in a dapper suit.
Flavia, 34, and Jimi, 40, met when they were paired together on Strictly Come Dancing in 2010, and became engaged earlier this year.
Messages of congratulations flooded in from happy well-wishers. One said "Congratulations Flavia! You look stunning. And Jimi is so cute!" while another fan wrote "congrats to u and Jimi you look amazing Flavia. May the rest of yr lives together be blessed with happiness & love."
Meanwhile, fellow Strictly star and Reveal astrologer Russell Grant - who partnered Flavia in the 2011 series - tweeted: "@FlaviaCacace just to let you know I'm in tears of happiness in my dressing room @lighthousepanto."
Former SCD judge Arlene Phillips spoke for all of us, when she said: "Never seen you look more beautiful. Xxxx"
Flavia immediately changed her name to Flavia Cacace-Mistry on her official Twitter account - too cute!
Did you think Flavia and Jimi make a beautiful couple? Tell us below!