Since filming Titanic in their early 20s, the duo have remained close.
In this week's issue, Winslet, 40, tells PEOPLE that DiCaprio, 41, has changed since they first worked together, but he's still the same Leo who stole the hearts of many nearly 20 years ago.
"He's a solid, loyal person," Winslet says. "He's a great friend, he always has been, and not just to me, but to everyone around him. He still has friends he had when we made Titanic."
The Steve Jobs actress adds, "In many ways he hasn't changed a bit, but in other ways he absolutely has changed."
"He's a stronger actor in this moment than he's ever been," says Winslet, who also costarred with DiCaprio in 2008's Revolutionary Road. "I think he's more handsome than he's ever been. And he feels, to me, the most settled he's ever felt, in himself, right now, which is quite strange, really, given that there's a lot happening around him."
For much more about Leonardo DiCaprio, pick up the new issue of PEOPLE, on newsstands Friday
DiCaprio has been picking up award after award this season, including a Golden Globe and a Screen Actors Guild Award, for his role in The Revenant. The film is also nominated for 12 Oscars, while Winslet is herself up for a Best Supporting Actress Oscar for her role in Steve Jobs.
The two pals have recently been spotted together at awards shows, thrilling many of their may fans.
"He's quite centered and calm, and that's different to the way he was 20 years ago," she says.
Reporting by MARY GREEN