Talk show host Oprah Winfrey says she was surprised by how open Prince Harry and Meghan Markle were in her interview with them.

During their explosive March 7 interview, the couple accused the royal family of racism, revealing there were "concerns" over their son Archie's skin color. Meghan also opened up about feeling suicidal and not being able to get help.

"I had no idea that (the interview) would have the reverberating impact that it has had and continues to have," Winfrey said.

The 67-year-old media personality, who is known for drawing out her interviewees, was speaking on The Nancy O'Dell Channel which launched last week. She was promoting her new book, What Happened To You? Conversations on Trauma, Resilience, and Healing, which is available from Tuesday (April 27).

Winfrey said she did a lot of preparation for the royal interview and also put in time and effort to ensure there were no leaks.

"I remember when we finished doing the interview, and that interview was 3 hours and 20 minutes I think, I stood up and said to the crew, 'We all know what was said here and how important it is to have a trust to the people who just shared that so I'm hoping you all will not go out into the world and share what has happened here.' And nobody did," she said.

She revealed that she did not meet the couple prior to the interview, although they did exchange messages as she wanted to know what their intentions were.

"Our shared intention was the truth. They wanted to be able to tell their story and tell it in such a way that allowed them to be as truthful as possible," she said.

When asked if she was surprised by how forthcoming Meghan, 39, and Prince Harry, 36, were, Oprah replied: "I was surprised. What? You're going there? You're going all the way there."

She also shared why she thought it was such a powerful interview: "What makes it powerful is when you have somebody else who is willing to be as open, as vulnerable, as truthful as they were. The reason the interview was what it was because they answered the way they did."