Royal wedding guest Serena blushes at timing of 'Queen is back' ad

'Nike came up with this idea right when I decided I was going to come back. And so it's kind of interesting how it all tied into the wedding and, you know, then I felt a little awkward!'

Few people can upstage American tennis great Serena Williams but even the 23-time Grand Slam champion knows one should never steal the show at a friend's wedding, not least a royal wedding.

So the timing of Nike's advert "the Queen is back", launched to coincide with the first-time mother's return to the French Open, was, she said, a touch embarrassing.

"Nike came up with this idea right when I decided I was going to come back. And so it's kind of interesting how it all tied into the wedding and, you know, then I felt a little awkward!" Serena told a news conference after stunning the Roland Garros crowds with her all-in-black catsuit.

"Now, you know, Meghan is royalty and I have known her for so many years, and I'm like, I'm not -- now she's a princess. A duchess, I should say, excuse me."

"But anyway, it's all really cool."

Serena joined Queen Elizabeth, senior royals and celebrities including Oprah Winfrey, George Clooney and David Beckham at the marriage of Prince Harry and his actress bride Meghan Markle earlier this month.

The ceremony in a medieval chapel at WindsorCastle blended ancient English ritual with African American culture, breaking with tradition, in particular the passionate sermon of US Episcopalian bishop Michael Bruce Curry that was far removed from the sombre tones of the Church of England.

"You know, it was really exciting to see so much African-American culture impacted in the wedding, and I was really happy that Meghan wanted to incorporate that into it," Serena said.

"I think it was just a whole cultural shift and change. It was seeing how far African-Americans have come, I thought it was an incredibly inspiring and beautiful and really motivating thing."

But she poured cold water over British media stories that she ran a beer pong table at which she used her tennis skills to come out on top.

"Oh, there was no beer pong. I don't know where this story (came from) -- I don't even drink beer."