Story highlights Jane Merrick: What makes this royal couple special is the way Harry has broken out of the tight constraints of royal protocol

In Markle, young girls in the UK and US have a role model who is not a princess but an independent-minded feminist and career woman, Merrick says

Jane Merrick is a British political journalist and former political editor of the Independent on Sunday newspaper. The opinions expressed in this commentary are hers.

(CNN) Just as Princess Diana broke down the stuffiest of royal traditions and conventions, her younger son -- and his new fiancée -- are modernizing the royal family all over again.

Prince Harry's engagement to actress Meghan Markle is not the first to join a senior member of the British royal family with an American, nor with an American who has been married once before. The comparisons between their engagement and that of Edward VIII, who gave up the throne so he could marry divorced American Wallis Simpson, end there, however.

What makes this royal couple different from any other around the British throne is the way Harry has -- with, it seems, the positive influence of Meghan -- broken out of the tight constraints of royal protocol to discuss grief, mental health and to share his searingly honest admission of not always wanting to be a prince.

Harry and Meghan began dating 18 months ago, and so it is surely no coincidence that the prince's transformation from someone who partied hard into a taboo-breaking royal role model has happened over a similar period of time. The watershed moment came in April of this year, when Harry gave an interview to the Daily Telegraph's Bryony Gordon about his battle with mental health problems following the death of his mother 20 years ago.

The significance of this moment cannot be overstated: for the many people who suffer from anxiety, depression and other mental health issues, one of the toughest challenges can often be talking about it openly. It is still, in our modern society of social media sharing, a taboo for many. For a member of the royal family, whose members guard their private lives as closely as their crown jewels, such openness was extraordinary.

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