Serena Williams has hinted that she will be a guest at the royal nuptials - posting a picture of herself in a towel "getting ready for my friend's wedding".
The tennis star was rumoured to be attending Prince Harry and Meghan's big day.
Now she has shown fans an image of herself wearing just a white towel on Instagram.
She wrote: "Follow my Instagram stories today to see me getting ready for my friend's wedding #beingserena."
Meghan's Suits co-star Patrick J Adams is in the UK and said that he was already getting emotional even before watching his friend "take this monumental step".
He tweeted: "70 years ago my grandparents, Patricia and Cedric Marsh were married in a small service in Windsor, England. Just found that out. Already getting misty... #royalwedding".
The actor, who played Meghan's on-screen husband Mike Ross in the drama, posted a picture of Suits cast members seated around a table at a restaurant near to Windsor, where the bride-to-be will marry Prince Harry.
The 36-year-old Canadian actor captioned the image: "The last supper #royalwedding."
And he later wrote: "Going to bed now and thinking a lot about the strange surreal and wonderful day my friend Meghan is going to have tomorrow.
"Meghan - wherever you are - we are so grateful to be here to watch you both take this monumental step together. Love deeply and live well."
He and his wife, Pretty Little Liars actress Troian Bellisario, were previously pictured at the Royal Standard of England pub in Beaconsfield, Buckinghamshire, in a post on Instagram.
Two more Suits stars, Gabriel Macht, who plays Harvey Specter, and his wife Jacinda Barrett, who plays Zoey Lawford, have also been in the UK this week.
And Sarah Rafferty, who plays Donna Paulsen in the series, appeared on American TV programme Today live from Windsor to talk about attending.
She was joined on the programme by Rick Hoffman, who plays Louis Litt in the TV show, and Gina Torres, who plays Jessica Pearson.
They told the Today hosts they were delighted to be able to attend the wedding of their friend and former colleague.
Other former co-stars and friends of Meghan, including Abigail Spencer and Wendell Pierce, are rumoured to have been invited.
Indian actress and philanthropist Priyanka Chopra, a close friend of the bride-to-be, previously said she would be attending.
In the early hours of Friday morning, she posted pictures on Twitter from a transatlantic flight.
Alongside one picture, from her seat on the plane, the Quantico actress wrote: "C u on the other side."
And she later wrote on Instagram: "Pre-wedding shenanigans! 12:10am the morning of...and still waiting for the dress!"
Other showbiz names rumoured to be joining in the celebrations include Victoria and David Beckham, who were among the star guests at the wedding of the Duke and Duchess of Cambridge in 2011, and Sir Elton John and husband David Furnish.
Possible guests also include Ed Sheeran and Ellie Goulding, model Cara Delevingne and former Made In Chelsea star Millie Mackintosh.