Is Royal Mail guessing with new collection featuring Estimate?

Arkle, Frankel and Kauto Star would feature on many people's list of the greatest racehorses in the last 60 years, but hands up if Estimate makes the cut in your top eight.

A special series of Royal Mail stamps celebrating eight legends of the turf, to be released on Thursday, is likely to provoke consternation among fans of Mill Reef and Dancing Brave, a notable pair among the legends who have been overlooked in favour of the Queen's 2013 Gold Cup winner.

In January it was announced that four-time King George VI Chase winner Desert Orchid, who also won a Cheltenham Gold Cup, would feature among the prints, but the remaining seven stars were not revealed until Saturday.

They include the mighty Frankel, unbeaten in 14 starts and regarded as one of the best Flat horses of all time, Shergar, who bestrode the turf in 1981 with emphatic wins in the Derby, Irish Derby and King George King George VI and Queen Elizabeth Stakes before being kidnapped, and Brigadier Gerard, the 2,000 Guineas winner in 1971, who captured the King George the following year.

The new stamps will be available from Thursday

Arkle, winner of three Gold Cups and widely acknowledged as the greatest jumps horse in history, is remembered, along with Grand National legend Red Rum, the only horse to win the sport's most famous race three times.

Kauto Star, a modern-day great with five King Georges and two Gold Cups on his CV, is also celebrated, but it is Estimate's addition that will raise eyebrows.

Trained by Sir Michael Stoute, the mare's finest hour came in the Gold Cup at Royal Ascot in 2013 under Ryan Moore – her only top-level victory.

One man who was certainly not amused by Estimate's inclusion is Racing Post historian John Randall, who was consulted during the selection process.

He said: "How can the Royal Mail be so misguided? Its choice of Estimate as one of British racing's eight legends in its new issue of stamps, along with seven authentic giants of the Turf, is embarrassing.

For a sub-standard Ascot Gold Cup winner to be given this ultimate accolade at the expense of Mill Reef and Dancing Brave, just because she happened to be owned by the Queen, is absurd."