Bride by Default (The Choice That Was Always Hers) by Dakota Quinn

One reckless night. No names. No promises. Aviation executive Sienna Hartwell told herself there would be no consequences.
She arrives at her sister’s grand cathedral wedding, only to freeze when she locks eyes with the groom. The stranger she walked away from in a Heathrow hotel bed is Adrian Swift — billionaire airline magnate, and her sister’s fiancé. A ruthless hidden debt covenant leaves Sienna as the only person qualified to save her family’s crumbling aviation empire. With no other way out, she steps into her sister’s bridal place at the altar.
Minutes after saying "I do", Adrian leans in and murmurs against her ear: "Tonight, you're going to invite me in. You just haven't realized it yet."
Now Sienna is trapped inside a hastilydrafted marriage contract she never fully scrutinized, haunted by their explosive anonymous encounter, and tangled in a web of corporate sabotage she barely understands. Adrian Swift always seems three moves ahead, anticipating every choice she makes before she makes it.
Is she merely saving her family’s business or has she walked straight into a trap that was laid long before she ever set foot in that cathedral?