The man who sold boom colt Zoustar for $20 million this week was so overcome with the joy of the three-year-old's Coolmore Stud Stakes win he fainted in the mounting yard at Flemington.

Syndicator Sheriff Iskander said nothing like it had ever happened to him before.

"I don't get excited about anything. I just don't know what happened," he said.

He said the monumental decision to sell Zoustar, combined with jockey Jimmy Cassidy celebrating his 100th Group One win on the horse, may have caused the brief faint.

"The excitement, the relationship with the horse, everything combined just got too much for me," Iskander said.

"I've never been so embarrassed in my life."

He said he had no regrets selling Zoustar to the Widden Stud.

Zoustar's sire Northern Meteor, winner of the 2008 Coolmore, died of colic at Widden at the end of July after securing the champion first season sire title and interest in his star's son had been intense.

Iskander said Zoustar could now go and realise the unfulfilled potential of Northern Meteor.

"This is a very serious racehorse - his looks, his temperament - everything about him is like Northern Meteor," Iskander said.

"Potentially, Northern Meteor could have been the next Fastnet Rock, so I hope this guy will go on and fulfill that."

Trainer Chris Waller will continue with Zoustar with a trip to Royal Ascot in June on the wish list before the colt is retired to stand at stud in the spring.