Meghan Markle's husband Prince Harry also speaks about the strain on him (AFP Photo)

Meghan Markle, the Duchess of Sussex, has revealed that her friends had warned her against marrying Britain's Prince Harry because of the harsh attacks expected from British tabloids.

The 38-year-old former actress, who opened up in a new documentary aired on the UK's ITV channel on Sunday night, also spoke of her struggle as a new mother to baby Archie while being in the media spotlight as a member of the royal family.

"When I first met my now-husband my friends were really happy because I was so happy. But my British friends said to me, ''I'm sure he's great but you shouldn't do it because the British tabloids will destroy your life''," said Markle.

"And I very naively - I'm American, we don't have that there - said, 'What are you talking about? That doesn't make any sense. I'm not in tabloids.'' I didn't get it. So it's been complicated," she said.

In the emotional documentary, the new Duchess referred to her life under the media glare as a newlywed and a new mother and regretted that "not many people have asked if I'm OK; but it's a very real thing to be going through behind the scenes".

On whether she feels she can cope, she adds: "In all honesty I have said for a long time to H - that is what I call him - it's not enough to just survive something, that's not the point of life. You have got to thrive".

Her husband, Harry - the Duke of Sussex, also speaks about the strain on him and the perceived rift with his brother Prince William for the first time.

"We are brothers. We will always be brothers. We are certainly on different paths at the moment but I will always be there for him as I know he will always be there for me," said Harry, the sixth in line to the British throne.

He was asked if he worried whether his wife may face the same pressures as his mother, Diana, Princess of Wales, who died in 1997 in a car crash in Paris.

The 35-year-old said: "I will always protect my family, and now I have a family to protect. So everything that she [Diana] went through, and what happened to her, is incredibly important every single day, and that is not me being paranoid, that is just me not wanting a repeat of the past. Part of this job is putting on a brave face but, for me and my wife, there is a lot of stuff that hurts, especially when the majority of it is untrue," he said.

The documentary focused on the couple's recent tour of southern Africa, during which it had been announced that Meghan Markle is taking legal action against the 'Mail on Sunday'' for publishing a letter she wrote to her estranged father, Thomas Markle.

Meanwhile, Prince Harry is suing the owner of 'The Sun'' and the now defunct "News of The World'' and "The Mirror'' over phone hacking allegations and has filed papers at the High Court in London.