LONDON -- Almost 3 billion people around the world are expected to tune in to watch the royal wedding on Saturday. More than 100,000 people will gather in the streets around Windsor Castle, hoping to catch a glimpse of Prince Harry and Meghan Markle in person. Among those well-wishers will be four women who first met at Tennessee State University more than 30 years ago. As CBS News correspondent Charlie D'Agata reports, they've traveled all over the world together since then, and this year they made the trip to London to be part of this once-in-a-lifetime event.

Tiffany, Margo, Debbie and Melanie have taken an annual vacation together for 15 years, and when they heard about the royal wedding, they couldn't pass up the chance to travel "across the pond" to see royalty up close.

Debbie Howard and Melanie Smoot were all smiles as they began their journey to London on Wednesday.

"They're young, they're hip, they're cool, he's marrying an American girl," Debbie told D'Agata after arriving in the British capital. "Go Meghan!"

They kicked off their big weekend of festivities with a champagne toast at their hotel; "to Meghan! To harry!"

Fashion and fascinators were very much at the forefront of the friends' minds -- and they had no intention to hold back: "It is the royal wedding. You have to be over the top!"

Like the rest of the world, they were still wondering on Friday what Meghan would wear.

"She is not going to do traditional," predicted Tiffany. "She is going to do something edgy."

Debbie said she foresees a "straight line with lace," and hopes the royal bride will don something that belonged to Harry's late mother, Princess Diana.

Perhaps most important for the American group, is how Meghan Markle -- a biracial American actress -- might change the British royal family.

"I think their love signifies diversity," said Margo. "By him choosing his bride and she is African-American, just makes it the best," said Margo.

"Her dreams came true. She got the prince," added Tiffany.

The friends have each bought new outfits for Saturday's big event -- hats and fascinators included. They planned to claim a spot outside Windsor Castle to catch a glimpse of the royal couple on what promises to be an historic day.