British royal Prince Andrew has broken protocol by issuing a public denial to dismiss rumours of an engagement to George Clooney's ex-girlfriend.

Prince Andrew, Duke of York, is rumoured to have struck up a romance with Croatian lingerie model Monika Jakisic after they were spotted having dinner together in London last month (Feb14).

However, reports of a royal engagement began circulating after Jakisic published a picture of a diamond ring sitting on top of a restaurant bill with the caption, "This is how it is."

The cryptic tweet has now prompted Prince Andrew's team to break royal protocol, which dictates they do not comment on family members' personal lives, to deny the story.

A representative for Prince Andrew says, "I can confirm the Duke of York is not engaged to Monika Jakisic."

Jakisic, who was first linked to Clooney in 2004, later took to her page to insist the picture was a reference to another couple celebrating an engagement.

Prince Andrew, the son of Queen Elizabeth Ii, was previously married to Sarah Ferguson.