Sheikh Mohammed says the trainer at the centre of a doping scandal which blighted his Godolphin racing team will never work with his horses again.
Speaking for the first time about the steroids affair, the ruler of Dubai told the BBC that the truth would emerge from an ongoing inquiry.
Trainer Mahmood Al Zarooni was given an eight-year ban in April 2013 for administering banned anabolic steroids to racehorses at a stable in Newmarket.
"I was shocked," Sheikh Mohammed said.
"I have many trainers and if one of them does the wrong things, you know - they gave him eight years, and I gave him lifetime. Finished."
Asked if he had seen the trainer, who has not spoken publicly since the ban and dropped a planned appeal, Sheikh Mohammed said: "He comes and sees some other friends but he will never come near horses."
A British Horseracing Authority inquiry found that 22 horses trained by Al Zarooni had been given illegal steroids, including St Leger winner Encke and 1,000 Guineas contender Certify.
All those horses were banned from racing for six months, and assistant trainer Charlie Appleby later took over the running of Moulton Paddocks.
In September, there was fresh controversy centred on endurance racing, with former London police chief Lord Stevens called in by the sheikh's wife, Princess Haya, to oversee an internal inquiry into the sheikh's worldwide equine interests.
The move followed the seizures of illegal veterinary drugs from a stables near Newmarket and a private jet at Stansted Airport.
On Sunday, Sheikh Mohammed gave a wide-ranging interview to the BBC at a Dubai desert location on a variety of subjects, from politics to business.
The sheikh was asked how horses could have been doped without his knowledge when he is famed for his attention to detail.
"He doped them not for racing but for treatment for the long term and they would not come to see the races. Now Lord Stevens will find out the whole story and we will all know what happened," said Sheikh Mohammed, who is thought to be the world's biggest racehorse owner, with hundreds of horses.
"We put an investigator, Lord Stevens, to really go through everything and meet everybody and I think he is independent and doing a good job. He hasn't finished yet but I hope good luck for him.
"The truth will come out because of independent Lord Stevens."
Al Zarooni claimed he thought the substances were allowed out of competition, as was then the case in countries like Dubai and Australia.
Sheikh Mohammed said that the use of anabolic steroids in all equine sport throughout the UAE had now been criminalised.
Asked if he felt his reputation had been tarnished by the drugs stories, he replied: "No. Of course if they think I know, I am clear and I still love horses and racing."