Deputy chairman Charles Rolls offloaded almost double the number of shares he originally intended to sell after receiving significant demand from institutional investors.
Shares dropped 5.4% to 2,796p in morning trading.
Rolls, who is co-founder with chief executive Tim Warillow, now owns a 8.6% stake in the company.
Since the company began trading on the stock market in late 2014, its shares have surged by more than 1,000%. In the past 12 months, shares have jumped by more than 90%.
Growing demand for gin and tonic boosted its 2017 results with adjusted underlying earnings (EBITDA) rising 64% to £58.7mln and revenues increasing 66% to £170.2mln.
In the annual results statement last Tuesday, Warrillow said the company has had an "encouraging start to 2018 and remain confident that we are increasingly well positioned to deliver further growth across the business".