United Kingdom, Feb. 1 -- Kaia Gerber and Lewis Pullman made a determined effort to keep their romance "under wraps".

The 23-year-old model started dating Lewis, 32, in December after she split from movie star Austin Butler - but the celebrity couple have made a conscious effort to keep their burgeoning romance out of the spotlight.

A source told Us Weekly: "Kaia and Lewis have actually been together for a while now.

"They started dating in early December. They kept it under wraps until the news of her and Austin's split came out. Kaia and Austin have been broken up since October."

Kaia and Lewis enjoyed a series of dates around Los Angeles in December, but the brunette beauty - who is the daughter of model Cindy Crawford and business...