Fox Corp said it had filed a suit against Flutter Entertainment related to exercising its option to buy a 18.6% stake in U.S. sports betting firm FanDuel Group.

Fox wants to pay the same price for the stake in FanDuel as Flutter had paid in December, while the latter has argued that Fox must pay a “fair market value”

Flutter, which merged its U.S. business with FanDuel in 2018, had raised its FanDuel holding to 95% in December in a $4.18 billion deal.

The dispute ties back to a deal the two companies made when Flutter was acquiring the Stars Group in 2019. Fox, which already had a business venture with Stars, agreed to acquire an option on an 18.5% interest in FanDuel, a business Flutter controlled.

Fox Chief Executive Officer Lachlan Murdoch said at an investment conference last month that the two companies have differing opinions on the exercise price of that option. Murdoch said the valuation should be based on what Flutter paid the minority shareholders of FanDuel for their stake last year.