Hoskins said he had no idea why his son was on the road when he was hit between 4.30am and 4.50am.
William had attended the wedding of a cousin the previous night and he assumed he had been trying to walk back to the Riverside of Cambridge Motel and Conference Centre after drinking with friends.
The distraught father said he hoped justice would be done and was angry that he couldn't attend the court appearance last Thursday.
He claimed no one had told him it had been brought forward from Friday.
"I only found out afterwards from Victim Support that it had been and gone, and that the man will be back in court next month.
"I'll definitely be there. I want to see his face."
The deceased was a popular man who enjoyed rugby and music. He had worked for his father's concreting company JMC Concrete in Hastings for the past five years after finishing an electrical apprenticeship.
"I still can't work out what happened to William because I was on that road just a few hours earlier and the conditions were fine. You could see for miles," Hoskins said. "This is an absolute tragedy for the whole family."
Hoskins was found injured and bleeding by a motorist. He was still breathing when emergency services arrived but died shortly afterwards.