An impulse purchase four years ago could pay handsome dividends for England rugby star Mike Tindall in Saturday's Grand National Steeplechase.

When Tindall raised his hand to start the bidding for a tiny five-year-old horse called Monbeg Dude in the late stages of a bloodstock auction at Cheltenham in May 2010, the last thing he expected was to be paying out £12,000 (HK$154,000) for him later that evening.

"I thought I would be outbid," Tindall said. "But the bidding suddenly stopped."

As it turns out, "The Dude" is proving to be an absolute bargain for Tindall and his fellow owners, professional rugby players James Simpson-Daniel and Nicky Robinson.

The winner of the Welsh Grand National in 2012, the gelding has since claimed two victories at Cheltenham and is now one of the favorites for the Grand National at Aintree, the world's most famous and gruelling horse race whose prize money has jumped to £1 million this year for the first time.

I thought I would be outbid. But the bidding suddenly stopped
Mike Tindall on when he bought Monbeg Dude four years ago

The 40-horse race is known as the toughest test of jumping in the world, with 30 fences over a four and-a-half mile course.

A sell-out crowd of 71,000 fans will be at Aintree for the 167th running of the National, the highlight of a three-day festival that began on Thursday. The race will be screened to a worldwide TV audience of about 600 million and bookmakers estimate about £350 million will be bet on it in Britain alone - five times more than is wagered on the English Derby. The National is always under scrutiny because of the potential for horse fatalities but modifications to the course ahead of last year's race, which included softening the high fences and improving landing areas and course irrigation, appear to have improved the situation.

Last year, all the 40 horses returned safely and only two fell. Only 17 horses finished the race but there was no repeat of the carnage that marred recent Nationals, with two horses dying in the 2011 and 2012 editions. Twenty-one horses have died over the Grand National fences since 2001.

Tindall, a member of England's World Cup-winning rugby team in 2003, only became interested in horse racing once he started dating Zara Phillips, the granddaughter of Queen Elizabeth. They married in 2011.

Phillips, who won a silver medal in equestrian in the London Olympics in 2012, has played a part in Monbeg Dude's rise, helping the horse with his jumping technique, which was deemed to be weak.