The TV stylist was pictured driving away from Scott's restaurant in London with 70-year-old Charles in the back of her car.
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They had enjoyed a meal together at the upmarket Mayfair restaurant with a friend – then left separately before the 49-year-old presenter picked up the advertising mogul. They reportedly then went the short distance to his Chelsea home, where Trinny stayed till the next morning.
The outing marked the third time they have been to the restaurant together in the past couple of weeks.
There has been no official confirmation of a romance between the pair, who are both divorced.
Charles' marriage to TV chef Nigella Lawson was ended in July, the month after he was photographed with his hand around his wife's neck at the same restaurant at which he has been seen with Trinny.
He initially dismissed the incident as a "playful tiff", but later released a statement to say that the marriage was over and that he was seeking a divorce.
Trinny split with her businessman husband Johnny Elichaoff in 2008 after ten years. She then moved on with Italian businesman Stefano Bonfiglio, but the pair went their separate ways at Christmas.