It was reported last month (Apr13) that the pop hunk, 19, had struck up a romance with the 33 year old, who shares a young daughter with actor Benicio del Toro.
Neither star has commented on the rumours, but the Maggie May hitmaker addressed the gossip during an appearance on British talk show Alan Carr: Chatty Man on Friday night (17May13).
When asked if Styles had stayed at his house, Stewart coyly replied, "Oh, that would be telling, I can't tell you that", before adding: "His car was there in the morning, let's put it that way. But he may have just come round to pick something up. She's allowed to do whatever she wants so I stay out of it. It's her life. He's a lovely fella."
He then exclaimed, "B**locks, I've let the cat out of the bag now! He was actually round for dinner last night, he's lovely... he couldn't be kinder, a funny guy. He's brilliant."