The Made in Chelsea couple have been dating for a mere six months but say they are going from strength to strength, having just moved in together.
And talk now appears to be on a possible wedding, as Harry reveals that Melissa has made some very firm hints as to what type of diamond she would like if he were to pop the question.
"Melissa has sent me a photo of the engagement ring she wants – it’s £150,000," Harry told OK! "I’ll have to remortgage my life!' Harry quipped."
Although he says he's sure she's joking with him to an extent, "there's a serious element to it."
Perhaps the pair are keen to jump on the nuptial train after seeing fellow Made in Chelsea alums Spencer Matthews and Millie Mackintosh tie the knot with their respective partners in recent weeks, with newlywed Millie only beginning to share some of the pictures from inside her big day with fans.
Millie and fiancé Hugo Taylor exchanged vows in early July joined by friends, family and ex-castmates of the London-based reality series - including Spencer Matthews who attended with his wife Vogue Williams.
"This is the first relationship I’ve had where we completely get each other," Harry said of his relationship with Melissa.
"Everyone thinks I was hooking up with girls left, right and centre, but it wasn’t like that. I’m actually a relationship person."
The full interview features in the 7 August edition of OK! Magazine.