"For about a week, we thought we had triplets, but sadly on the next visit to the doctor's, we only heard two heartbeats," Dion, 42, tells Hello! magazine in its current issue.
"That little baby decided to leave the space for the two others and to say goodbye to us," she says. "It happened very early during the pregnancy, but still, it shocks you."
But now Dion says she's currently in a good place. "[Motherhood] is going well," she says. "I don't get a lot of sleep ... For sure I'm tired, but that's what I want. And it's only for the first month or so."
Dion says even though her little ones were just born, they're already demonstrating character.
"One is more gutsy than the other," she says. "Nelson seems to have a little stronger personality right now. He's the tougher of the two."
Dion continues, "They are fraternal twins, but they look very alike. Nelson weighed more at the birth, but the doctor told us in a week or two, they're going to be the same."