Kate Lechowicz, the sister of Eric's fiancé Izabela, told the publication: "They were scheduled to fly together again in November just a short time after the helicopter crashed.
"[Prince] William had told Eric, 'Next time it will be with Kate and the kids,'" Kate told The Sun.
"He said it will be a nice day out for him and the family."
Vichai was well-loved by Leicester City fans, and William counted him as a personal friend and knew him through his role as President of the Football Association as well as a fellow polo player.
In November 2018, William and Kate were so moved by the incident they attended a service at Leicester City Football Club's King Power Stadium to pay tribute to those people who'd died in the crash, and they praised the "warmth and compassion" in the city following the tragedy.
"Prince William loved flying and he got on really well with Eric – they had flown together a number of times," Kate Lechowicz shared, speaking ahead of travelling to a private ceremony to mark the one year anniversary of the accident.
"He told me he loved his quirky sense of humour and had huge respect for his abilities as a pilot."
A report by the Air Accidents Investigation Branch (AAIB) found the helicopter crash, which occurred shortly after taking off from the pitch at the King Power stadium, was caused after a pin became disconnected in the tail rotor, meaning the helicopter became unstable.
The problem meant the tail rotor on the the Augusta AW169's became disconnected from the pilot's pedals, leading it into an 'uncontrollable' spin, the report found.
Prince George is following in his father's footsteps, and is a huge soccer fan.
The little royal was caught on camera last month as he celebrated a goal while watching his beloved Aston Villa Football Club play.
The adorable royal watched his favourite team take on Norwich City with parents, Prince William and Kate Middleton, and sister Princess Charlotte.
Kensington Palace later posted a video of George’s reaction on their official Instagram page.
The Duke of Cambridge has been a long-time support of Aston Villa and is regularly spotted at matches.