(a) - Confident, glamorous and professionally successful, Meghan Markle brings a modern face to Britain's royal family with her marriage to Prince Harry -- but both sides will need to adapt, commentators said Wednesday.

Queen Elizabeth II led the congratulations this week when her grandson was confirmed to be marrying the 36-year-old American actress, an outspoken feminist of mixed race.

Commentators hailed their union as a sign that the monarchy was keeping up with an increasingly multi-national, ethnically diverse Britain, viewing it as a breath of fresh air for an ageing institution.

But many noted that Harry's mother Diana was also feted as a fresh face when she married heir to the throne Prince Charles -- and that relationship did not end well.

"Could Meghan be similarly crushed? Or will she be given the oxygen to thrive? It is a test the institution can little afford to fail," wrote one commentator in the Daily Telegraph.

He suggested that when Charles takes over as king, he should "see her as an invaluable weapon in making the case for a 21st-century monarchy. How much harder now to accuse them of being out of touch".

- 'Very brave step' -

Markle has said she is ready for the "next chapter" after giving up her job in US television series "Suits" to marry Harry and move to Britain.

"I think she's taking a very brave step," royal biographer Penny Junor told AFP.

"She is giving up a fantastic amount that she worked for all these years. I have no idea if she will find royal life restrictive, dull or repetitive -- because it can be.

"I hope that she doesn't feel that she is hemmed in and caged."

But Markle is very different from Diana -- she is older, has already been married once and has had both a professional career and travelled the world as an advocate for the UN women's agency.

Markle will give up her UN work but will likely continue in humanitarian activities, which sits well with the royal family's focus on charity.

Her focus on gender equality has taken her into politics, however, notably when she described US President Donald Trump as "misogynistic" before he was elected.

She will have to be more careful now she is part of the royal family, which royals themselves reportedly refer to as "The Firm".

"If you join The Firm, you have to abide by its rules. That's where Diana started to go a bit wrong -- she was going off piste," Junor said.

"It's fine for her to have strong positions, but expressing them publicly is not risk free," added one commentator in The Sun tabloid.

"She can expect pushback from the public and potentially even politicians if she is seen to be entering sensitive political areas."

- 'Capable of anything' -

The monarchy has also changed since the days of Diana and her sister-in-law Sarah Ferguson, who also struggled once she married Prince Andrew.

Harry and his older brother William have forged a different path to their father Charles, adopting a more informal approach to royal duties while also trying to maintain a semblance of a normal private life.

They both have a strong sense of his mother's difficulties, and Harry has made clear he understands the pressures on his new fiancee.

"It's a big deal. It's not easy for anybody. But at the end of the day she chooses me and I choose her and whatever we have to tackle together or individually, we'll always be together as a team," he said.

"I think she's capable of anything."

© Agence France-Presse