Kelly Klein became a first-time mom last year at age 50, adding a bundle of joy into an already charmed life. On Thursday evening, October 23, at Hermès in Manhattan, she celebrates the publication of her newest book, Horse, from Rizzoli —$150 for the regular volume; the slip-cased deluxe edition is $400 — all profits going to the Equestrian Aid Foundation, which helps people in the equestrian world when they are severely ill or suffer catastrophic injury. Here, Kelly talks motherhood, career, love, books and how to be best friends with your ex-husband (designer Calvin Klein with whom she was having dinner after the Hermès book party.)

ETCETERIST: No one believes that you are 50, let alone 51 now, and everyone wants to know your beauty secret.

KELLY KLEIN: No beauty secret, no special facial products. I do eat healthy and exercise but, really, it is my parents, the good fortune of having their genes. They both have great skin.

ETC: You became a mother at 50 by surrogate, a beautiful baby boy named Lukas Rector, your maiden name. I know, and I have read, most recently in Town & Country, that you decline to discuss the details of this surrogacy, except that Lukas is your baby and that you were in the delivery room when he was born and that surrogacy for you has been the most amazing, wonderful experience. But what, so far, has been the biggest surprise of being a first-time mother?

KK: I sat on the fence for a long while thinking about having a baby. I wanted to work, I wanted to travel, I wanted to be able to ride and compete, but then, at age 48, I felt it was the right time. It took me a couple of years to figure it out, but when Lukas came my biggest surprise was realizing there was nothing for me to be fearful of all those years. This is the best thing that has ever happened to me. Why was I scared? I don’t know, something deep inside, I suppose.

ETC: He’s a good baby, as they say?

KK: Yes, very easy, and very, very independent.

ETC: It has been years since you worked on Seventh Avenue, first for Ralph Lauren and then for Calvin Klein, but you are still taking fashion photographs for various magazines, doing your books and riding?

KK: I compete in the Amateur Owner Hunter division. I just finished my last competition in Middleburgh, VA, and begin again in January in Palm Beach.

ETC: What is a typical day like for you?

KK: (She laughs.) Well, Lukas wakes up at around 5:30 and babbles in his crib until I get there at around seven o’clock. He’s very patient. He comes with me to my studio or with me on appointments, or to the horse shows. Once a week we go to music appreciation classes on the West Side near Julliard.