Graffiti artist Pegasus poses with his painting of Britain's Prince Harry and his fiancee Meghan Markle on the wall of a brewery in Windsor. Picture: Reuters

Meghan Markle knew Prince Harry was "the one" almost instantly, according to her close friend Janina Gavanka.

The 'Suits' star fell for the flame-haired royal - who she will marry in a ceremony at St. George's Chapel, Windsor Castle on Saturday May 19 - pretty quickly, according to her long time friend Janina Gavanka.

Speaking on 'Inside the Royal Wedding: Harry & Meghan', she said: "She had just started dating Harry and it was quite clear that that was her guy, that was her one."

And Janina has revealed it was seeing Harry get stuck in with charity work in Botswana that really sealed the deal for Meghan.

She added: "They were staying in a tent with nothing and just had each other. 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. They fell in love with nothing around them - no frills, no bells and whistles. All they had was each other, doing good work in a place where nobody was watching them."

The sweet comments about the pair's bond comes after it was revealed that Sir Elton John is expected to perform at the wedding.

Sources close to the 'Rocket Man' hitmaker told TMZ it is unclear whether he will perform at the church ceremony at St George's Chapel, Windsor Castle, or at their reception, which will be held at St George's Hall.

Elton initially had Las Vegas shows booked for this weekend but he pulled out of them months ago due to a "scheduling conflict".