The celebrity duo, who found fame on the reality TV show ‘Made In Chelsea’, got engaged during a recent holiday to Mykonos, Greece.
“I can confirm that Hugo and Millie did get engaged whilst they were on holiday in Greece,” a representative for the Taylor told MailOnline.
Mackintosh shared a photo of herself wearing a giant diamond on her ring finger on Instagram on Monday 31 July.
Mackintosh, who has her own fashion label, was previously married to musician Professor Green, but filed for divorce just over a year ago, after three years of marriage.
She reunited with Taylor - having previously dated when they were younger - last year.