Neil Patrick Harris revealed why he doesn’t want to know which twin is biologically his

Neil Patrick Harris once revealed why he doesn’t want to know which of his twin children is biologically his.

The 51-year-old How I Met Your Mother star tied the knot with husband David Burtka, 49, a decade back in 2014 after first going public with their relationship in 2007.

They became parents to twins Gideon and Harper - who are 14 years old - after a surrogate carried and gave birth to them in 2010.

The children are non-identical, as two separate eggs were used.

Neil Patrick Harris and David Burtka with their children, Harper and Gideon (Instagram/@nph)

Harris and Burtka, who is also an actor, each donated sperm in the hopes that either would fertilise the egg, but to their surprise, the twins were conceived.

Speaking to American broadcaster and journalist Barbara Walters in 2014, Harris explained: "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. Both took, miraculously."

Harris also explained that he has no interest in finding out which of his twins are his biologically.

He explained: "I have no interest in [finding out]. We are their parents and I love them implicitly."

While the couple have no idea about who the biological father is for each of their children, Harris said that they have suspicions 'based on their behaviour'.

However, the American Horror Story star did not reveal what those suspicions were, nor what child he thought could be his biologically.

Last week, Harris posted a family snap during Thanksgiving sharing a heartfelt message about what he felt truly 'grateful' for and fans were quick to comment on his and Burkta's children looking super grown up seemingly all of a sudden.

Fans couldn't get over just how 'grown up' twins Gideon and Harper looked in a recent family snap (Instagram/@nph)

One Instagram user penned: "Weren't they just 7 and 10?"

"Wait…I thought they were babies?! Omg time is going by way too fast!!" quipped a second, as a third exclaimed: "Kids are so grown up!! Beautiful family!"

"Wait wait wait - those aren’t the kiddos! No way!" chirped a fourth, while a fifth admitted: "I feel old I remember when you announced the birth of them!!!!"

Earlier this year, Harris took to Instagram to post a celebratory tribute to his hubby following the 10-year marriage anniversary.

He penned: "10 years ago, today. The time has flown. The family has grown. The chapters have been voluminous. The adventures, sublime.

"A decade can rip by, in an instant. David, I am delighted to spend my years, my days, my hours with you, and forever proud to have you as my husband. Happy anniversary, @dbelicious. You are simply resplendent."