Former Spice Girl Geri, 42, and F1 boss Christian, 41, have apparently booked swanky Kensington Palace as the venue.
A source told The Sun: "Geri wants to feel like a princess and for the bash to be as grand as possible. She's expecting around 300 guests."
Geri's royal choice could allegedly cost the couple a massive £14,500 to hire for the nuptials.
While it's unclear if any actual royalty will be present when Geri and Christian say 'I do' (she does know Prince Charles, after all), it's been claimed that the Spice Girls will reunite at the ceremony.
An insider previously revealed that Geri's band mates Victoria Beckham, 40, Emma Bunto, 39, Mel C, 41, and 39-year-old Mel B are all planning on attending.
The source said: "Geri is desperate for all the girls to be there. Some of their schedules are tighter than others but Geri's happy it appears they'll be a full-on reunion at her ceremony."
Geri and Christian announced their engagement in November, and both have children from previous relationships.