After receiving a phone call from his friend's hospital to confirm he was a match for his kidney transplant, Spencer revealed the incredible news to his friend of more than 20 years, Dave.
Unaware Spencer had even put himself forward, Dave was overwhelmed and overcome with gratitude. The transplant a success, Spencer wants to continue his support for Kidney Research UK, by raising money for the charity through Ride London.
Dave and his family will be watching from the sidelines and cheering him on - this is all the motivation Spencer will need to get him through.
The Ride London event takes place over three days from 28 to 30 July. You can find details of the BBC's live coverage of the event here, while the BBC Sport website will feature live text commentary of the Ride London 100 and 46 races and the men's elite London-Surrey Classic from 09:00 BST on Sunday.
And if you're inspired to try cycling yourself, check out our Get Inspired guide.