The 35-year-old Oscar-winning actress was rumoured to have dated Dowler, also 35, for four months last year after splitting from her husband Sam Mendes.
Now Dowler's grandfather Jack Pearce has confirmed they are back together and that the Revolutionary Road star has been spending time getting to know his family.
Speaking from his home in Cornwall, Pearce told UK newspaper, the Daily Mirror: 'They are on holiday down here. He brought Kate round yesterday and it is the first time I have met her. We went for a pub lunch.”
He added: 'She is a very attractive girl. She was polite and very friendly. They didn't talk to me much about their personal life, but they seemed very much together.'