Misha Nonoo, who reportedly recently separated from old Etonian Alexander Gilkes, is a close friend of the Suits star and holidayed with her in Spain over the summer.
She was also in the UK, posting photographs from the Royal Enclosure at Ascot to her Instagram account in June.
The New York-based designer is very well connected in royal circles and counts Harry's cousin Princess Eugenie among her friends since her time working for Alexander’s upmarket Paddle8 Auction firm in the US.
Alexander was a guest at the 2011 Royal Wedding of the Duke and Duchess of Cambridge and his younger brother Charlie is a former flame of Pippa Middleton.
Eugenie and her sister Princess Beatrice along with James Middleton were guests at his lavish three-day wedding to Misha in Venice in August 2012.
Harry is known to be very close to Eugenie, who also remains friendly with his last serious girlfriend, Cressida Bonas.
Nonoo is a CFDA/Vogue Fashion Fund finalist and fans of her eponymous line include Emma Watson and Cate Blanchett as well as her close pal Meghan. The designer hasn't yet responded to requests for comment.