Neil Patrick Harris on Having Twins With Husband David Burtka

Actor tells Barbara Walters they used an egg donor and a surrogate.

"We inserted one of my sperm and one of David's sperm into two eggs, with the hope that they would both take, just because we both wanted to be dads biologically, and both took, miraculously," Harris told Walters in an interview for the upcoming ABC News special, "Barbara Walters Presents: The 10 Most Fascinating People of 2014."

When it comes to his role as a parent, Harris said he thinks he's a good father.

"I'm a bit of the stern disciplinarian. My voice gets real intense," he said.

Harris is the father of one of their twins, and Burtka is the father of the other, but Harris said he has "no interest" in finding out which of his children is biologically his.

"It's so funny. I see myself in each of them at different times," Harris said.