Meghan Markle knew she had found 'The One' in Prince Harry just weeks into their romance, according to her longtime friend and fellow actress Janina Gavanka.

The former Suits star will wed the British royal in Windsor, England on Saturday (19May18), and Janina is one of the bride's close friends who managed to land an invitation to the nuptials.

In a new interview for U.S. TV special Inside the Royal Wedding: Harry & Meghan, the True Blood actress admits it didn't take long for Meghan to recognise her relationship with Harry was going to go the distance.

"She had just started dating Harry and it was quite clear that that was her guy, that was her 'one'," said Janina.

In another recent chat with ABC News, she recalled how her pal of 15 years was bowled over by how down-to-earth Princess Diana's youngest son was, after meeting up in Botswana, where they worked on conservation projects together.

"They were staying in a tent with nothing and just had each other...," Janina shared.

"I remember when Meghan told me about Botswana. I loved how she was... pleasantly surprised. Like, this boy is actually just doing this for real. This is not some flouncy trip... he really means it."

Their shared interest in making a difference in the world through philanthropy really helped the pair bond, and its "low-maintenance" approach to life is what Janina believes will form the basis for a strong marriage.

"They fell in love with nothing around them - no frills, no bells and whistles," she explained. "All they had was each other, doing good work in a place where nobody was watching them."

Noting Harry and Meghan's history of charity work before they even began dating in the spring of 2016, Janina added, "They did that separately. Imagine what they can do together."

Reports suggest the happy couple is planning to return to Africa later this year (18) for its honeymoon.