The Courtship Caper by Beverley Oakley

Widowed Sebastian Wells has spent a year searching tirelessly for the girl he was forced to give up after honour required him to wed another.

When he discovers Venetia working as a lowly companion to the exacting Dowager Duchess Lady Indigo at a Christmas house party he’s attending, their secret rendezvous turns scorching.
But Sebastian’s hostesses, the scandalous Brightwell sisters, have paired him up with a lively, golden-haired debutante they believe will be his perfect match. And this young lady is determined to make everyone believe the lie.
Will honour once again compel Sebastian to act against the desires of his heart?

The Courtship Caper is Book 6 in the Scandalous Miss Brightwell series but can be read as a standalone.