Julia Roberts is "a genuinely and deeply happy person."
The 47-year-old actress, who has 10-year-old twins Hazel and Phinnaeus and son Henry, eight, with husband Danny Moder, feels very fortunate to have "the natural chemistry of joy."
The Oscar winner said: "I am a genuinely and deeply happy person, which, as life goes on, you realise what great fortune that is, to feel like you just have the natural chemistry of joy."
Julia is known for her trademark smile, but says she can't explain it.
She said: "I don't think it's healthy or productive to self-analyse. The way a person smiles is the way they smile. It sort of becomes this thing: 'Let's see that smile.' I can smile or I can not smile, but I can't perform."
But the 'Pretty Woman' star credits Danny for much of her happiness.
She told the October issue of Allure magazine: "I don't know if I would have succeeded in some of the efforts that I made if he hadn't been in such close physical proximity to me. There's something about having the safest place in the world for you in the same room."
Meanwhile, the 'August: Osage County' star felt a "sweet shift" in her friendship with pals George Clooney, Brad Pitt and Matt Damon when she was pregnant for the first time.
Recalling how protective they became, she said: "It was such a sweet shift in our relationships because originally, it was all pranks and teasing each other. And here I am pregnant, so it's like pulling out my chair and just making sure I have enough water and, 'Are you feeling okay? You look a little peaked.' 'I'm fine.' "