Some 600 guests will be invited to the royal wedding, but only 300 will be invited to the crème de la crème evening event, Katie Nicholl, author of the book "William and Harry," tells ABC News.
"The ticket that everyone really wants -- and it is the golden ticket -- is the invitation to the evening reception which is being hosted at Buckingham Palace by the Prince of Wales," says Nicholl.
"[Prince] William and Kate [Middleton] have been told they can invite 100 each."
The size of the wedding is apparently not related to the capacity of Westminster Abbey, the official Church of the British royal family, which has enough seating for 2,000 people.
The royal couple is reportedly under pressure to finalize the guest list, which is set to be released in a couple of weeks.
"This is something that every bride and groom can relate to," says Nicholl. "I'm told that Kate's mother Carole, like every mother of the bride, wants to have as many of her friends there as possible."
This past weekend marked Kate's 29th birthday, her last as a commoner. She had a low-key weekend, celebrating with William, her friends and family.
"Kate's not a showy person," says Nicholl. "She doesn't want to be seen at night clubs, she wants to stay below the radar and she wanted to spend her birthday very quietly."
We don't know what birthday gift Will gave to his bride-to-be.
"Kate got sailing lessons for Christmas from Will," says Nicholl. "Perhaps a boat will follow?"
The main activity of the weekend was a friends' wedding which the royal couple attended. The high-society event -- at which more than 30 guests had titles -- was almost a practice run.
Kate wore a black dress with a very low neck-line to the marriage of friends Harry Aubrey-Fletcher and Louise Stourton. This diversion from the pastel and floral dresses often worn at weddings reflects Kate's unique style.
It is also not in step with her family-to-be: Members of the royal family only wear black for papal visits or funerals.
Another surprise to come is the choice of wedding dress for the event, planned for April 29.
Kate Middleton's Royal Wedding Dress
Elizabeth Emanuel, who designed Princess Diana's wedding dress, says he believes Kate's will be marked by simplicity and elegance.
"I would imagine she's going to go for something quite classic but with a little bit of a twist, with an edge to it," Emanuel tells ABC News.
"I don't think it's going to be quite theatrical as the one we did for Diana."