Grayson was PNE manager when they beat Swindon Town 4-0 at Wembley in the 2015 League One play-off final.
It brought about a return to the Championship for North End after four years away.
Grayson had nearly four-and-a-half years in the Deepdale hotseat and enjoyed working under Hemmings' ownership.
Now in charge of Fleetwood Town, he paid a warm tribute to Hemmings who died on Monday evening at the age of 86.
Grayson told the Lancashire Post: "First and foremost, my deepest sympathy to Mr Hemmings' family.
"It was such a shock to hear the news on Monday night.
"He was a person I really enjoyed working with. On a day-to-day basis, my dealings with Mr Hemmings were through Peter Ridsdale.
"But he was very supportive of what we tried to do.
"We would go on a few socials to race meetings and Mr Hemmings was really good company, young at heart and had a good time.
"From time to time he would come to the training ground to see everyone for a catch-up and to watch the training.
"Mr Hemmings was hands-on without being too hands-on if that makes any sense.
"He trusted Peter and myself to get on with things. Obviously he would have the major call on transfers because it was his money being spent."
The Wembley victory was a fine day out, Jermaine Beckford's hat-trick and a Paul Huntington goal sealing the win.
Said Grayson: "A lot of Mr Hemmings' success had been in horse racing with the three Grand National winners.
"So it was nice that we could give him that success in the football, reward the team effort put in throughout the club.
"It was great to see him afterwards with the trophy and then celebrating at Deepdale with us the following day."
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