One of London's most famous hedge fund managers just made millions with a genius bet on Sports Direct

One of the UK's most prominent hedge fund managers just made a very smart move, and made himself a whole heap of money in the process.

Crispin Odey, the boss of prominent hedge fund Odey Asset Management has just bought around 4% of shares in troubled retailer Sports Direct, less than a week after selling a similar chunk of shares in the same firm.

The news was first reported on Wednesday evening by the Daily Telegraph, and was confirmed in a regulatory filing on Thursday morning.

Essentially, what Odey has done is take advantage of Sports Direct's plummeting share price to make himself a healthy chunk of money.

The exact time of the purchase and how much the shares cost was not disclosed. But a very rough calculation done by Business Insider shows Odey could have made £15-20 million ($21.5-29 million) from his bet. The calculation was based on Odey selling his shares in Sports Direct on Friday morning when they were around £5.10, and buying them back on Tuesday afternoon when they were about £4, and doing so at market value.

According to the statement filed to the stock market on Thursday morning, Odey bought around 21.5 million shares, 3.6% of Sports Direct's total share offering, adding to the 8.6 million shares already under his control. In total, 5.05% of Sports Direct shares are in Odey's control, and he is now one of the firm's top 5 stakeholders.

Last Friday, in an interview with the Daily Telegraph, Odey said that he had reduced his stake in Sports Direct from roughly 5% to around 1.5% saying that he'd "seen the writing on the wall," and that as a result he'd decided to "lighten his load" in Sports Direct. Odey made the announcement just a few hours after Sports Direct issued a profit warning.

In the interview, he also said that Sports Direct boss Mike Ashley "can't be a happy beasty" and that Sports Direct's "share price over the last few weeks has indicated the direction of travel". Basically it seems like Odey then changed his mind massively over the last few days.

Sports Direct in the toilet

Sports Direct's shares have tumbled by nearly 50% in the last year, and have lost more than 30% of their value in just nine days of trading so far in 2016, losing more than £1.1 billion in market capitalisation. The big problem seems to be a lack of innovation, and a poor product offering, according to analysts, including Peel Hunt's Jonathan Pritchard.

However, a series of PR disasters also helped drag shares down. There are numerous incidents, but some of the biggest include: allegations of mistreatment of workers, Mike Ashley being sued over an unsettled bet, Ashley being accused of nepotism by giving his daughter's boyfriend a cushy job, and accusations that the company effectively pays workers less than minimum wage.

Crispin Odey is well known for his big bets on UK retailers. Most of them are successful, but some, not so much. Just last week, Business Insider's Oscar Williams-Grut reported that Odey Asset Management lost a huge chunk of cash after building up a big short position in Home Retail Group, the owner of Argos and Homebase.

When the news of an approach from Sainsbury's to buy the group emerged, shares in Home Retail rocketed, costing Odey's fund millions of pounds.