Gambling Insider understands Sky Bet lost around £3m ($3.9m) on the Supreme Novices' Hurdle, the first race of the Cheltenham Festival on Tuesday, which was won by Willie Mullins’ Klassical Dream at 6/1.

Sky Bet has been running a promotion throughout the Festival which allows its customers to have a risk-free bet of up to £20 on the first race every day. If a customer’s horse lost, their bet of up to £20 would be refunded as cash that can be withdrawn.

William Hill suffered on day three of the Festival, losing around £2.2m, Gambling Insider understands.

Heavy favourite Paisley Park was considered one of the best bets of the meeting and was very well supported on the day, costing William Hill £500,000 in single bets alone.

The seven-year-old triumphed in the Stayers’ Hurdle, which was one of the main reasons why punters came out on top on Thursday.

It is as yet unclear how other major operators fared on Thursday, but with three favourites winning out of five races, it is likely to have been a difficult day across the board.

Despite this, Al Boum Photo prevailed in the Gold Cup at 12/1, while Anibale Fly came second at 22/1 and Bristol De Mai back in third at 18/1, resulting in bookies potentially clawing some of those losses back.

Gambling Insider has reached out to Sky Bet for comment.