The former reality TV star was spotted with her former flame and Made In Chelsea co-star at the British Polo Day, which was held in Dubai on Good Friday (25/3/16).
Newly single Millie - who split from husband Professor Green last month - was seen with "her arms around" the 29-year-old and allegedly kissing her former beau.
A source revealed to The Sun: "They looked very cosy and seemed to be very close again."
Millie jetted out to Dubai for Easter weekend and has been keeping fans updated on her holiday antics with a number of Instagram snaps. The fashionista seemed to be enjoying the break with pals in a series of envy-inducing beach shots.
Meanwhile, Hugo also took to the social media app to post his own images of his time in the United Arab Emirates city.
The posh pair were an item on Made In Chelsea during series two of the show, but their relationship came to an abrupt end when it was revealed Hugo had cheated with fellow star Rosie Fortescue.
While Millie moved on with Pro Green, Hugo was in a relationship with Natalie Joel, who also appeared on the London-based show. But the duo parted ways in June 2014 after almost two years together.
Pro Green and Millie announced their separation in February, stating:
"It is with sadness and regret that we confirm our separation. It is a mutual decision, we still care deeply about each other and would like it to be known it is on amicable terms and we wish each other well."
Since the split, it's been rumoured that the couple split due to arguments over kids - with Professor Green wanting them, but Millie not quite ready to become a mother.
A source told The Sun: "Kids became a big problem. Millie didn't want them any time soon and he did. They loved each other but would have these crazy explosive rows."