Meghan Markle and Prince Harry. Picture: Instagram.

American beauty Meghan Markle has successfully "tamed" Prince Harry, according to royal expert Katie Nicholl.

The 36-year-old beauty is set to marry the British royal in May, and since she started dating Prince Harry in mid-2016, Meghan has helped to transform the previously rebellious royal, according to author Katie Nicholl.

The writer - who has penned the book 'Harry: Life, Loss, and Love' - explained: "I started charting Prince Harry's life 10 years ago now and there were tags that were attached to him.

"He was a bit of wayward royal, you know, there was a bit of a rebel in him. I would say that Meghan has tamed him. I think Meghan has changed him for the better. 

"I think she's helped get him more in touch with his emotional side and he is without a doubt a happier man with Meghan in his life."

Katie claimed that Prince Harry's bride-to-be has helped him to embrace the responsibilities and challenges that come with being a member of the royal family.

In fact, she argued that the 33-year-old Prince has "met his match" in the former 'Suits' actress, who he'll marry at St George's Chapel at Windsor Castle on May 19.

She told Entertainment Tonight: "When I see him on engagements now he's smiling, he's always been enthusiastic. He's always been charming, that is part of Harry's appeal. But he seems so much happier.

"So much more ready to embrace the future and his royal role with someone to share the load with. He seems really to have met his match in Meghan."

Meanwhile, Katie recently claimed that the loved-up couple will be looking to start a family in the near future.

She said: "Prince Harry, particularly, is very keen to start a family, pretty soon after the royal wedding."