BBC Radio presenter Jo Whiley will be switching her headphones for a helmet.
She will be the celebrity starter for Cycle 4 Cynthia at Althorp on September 23.
The event has raised almost £200,000 for the Friends of Cynthia Spencer Hospice and Macmillan Cancer Support, in the county.
Jo will also be leaping into the saddle herself and joining the hundreds of cyclists.
She said: “I also grew up close to Althorp, in fact I used to wash the dishes in the kitchen there, so I’m very fond of the park and of course the surrounding countryside and local villages which are really beautiful.”
There are five, 25 or 50 mile routes. Go to www.cycle4cynthia.co.uk for more and sign-up details.