Peter Chapple-Hyam has been chosen as the trainer of the most expensive yearling bought at auction in the world this year.

A half-brother to Authorized, the colt Chapple-Hyam trained to win the 2007 English Derby, Hydrogen cost Sheikh Fahad Al Thani's Qatar Racing 2.5 million guineas ($A3.985 million) at the Tattersalls sale.

The sheikh's 18 trainers gathered at a yearling parade at David Redvers' Tweenhills Stud on Sunday and were each given an envelope containing the names of horses that would join their stables.

"It's fantastic news and I am very honoured," Chapple-Hyam told the Racing Post.

"I didn't really expect to get him but thought I might be in with a chance. He was picked by a very good team so only I can let them down. I had seen him at the sales before today and he looks a lovely horse.

"It's a long way off but on his pedigree and everything else there is a big chance he could be a Classic prospect. It's a big boost. We are not a big stable so this is a real pick-me-up.

"It's like getting the golden ticket to Willie Wonka and the Chocolate Factory."

William Hill has priced Hydrogen at 8-1 to win a Group One as a two-year-old, 50-1 to win the Derby, 66-1 to win the 2,000 Guineas.

Sheikh Fahad is the owner of 2011 Melbourne Cup winner Dunaden and stands Makfi at Westbury Stud in New Zealand.