Debbie Bestwick, the co-founder of everplay group, has sold 3.33 million shares in the video games company, raising around £14.1 million.
The shares were placed with a small number of institutional investors at 423.5p each.
That is a discount of around 3.5% to Wednesday's closing price of 439p.
Bestwick, a non-executive director, built the business as Team17, the publisher behind the Worms series, before it was renamed everplay.
Still a major holder
She will keep a significant shareholding after the sale, though the company did not say how large it will be.
everplay said Bestwick remained highly supportive of its strategy and growth prospects.
The company said there had been sustained investor demand for its shares.
It added that the sale would improve liquidity, meaning how easily the shares can be bought and sold, and widen its base of institutional investors.
Bestwick has agreed not to sell any more shares for 180 days, subject to the usual exceptions.
The deal is due to settle on 5 October.
Jefferies, the investment bank, ran the placing.
