Neil Patrick Harris sparks reaction with before-and-after photos of rarely-seen twins

Neil Patrick Harris is one proud dad! The How I Met Your Mother actor shared adorable before and after photos of his twins to Instagram celebrating their 16th birthday and sparked a big reaction.

"Harper and Gideon turned 16 today…," Neil wrote to Instagram alongside four photos, two of the twins as babies and two of them all grown up. "It's amazing to see how they've grown, and I couldn't be prouder of the people they've become. Mostly, though, I'm so grateful that they can drive me around everywhere now."

He also added: "[Love] @dbelicious for being a remarkable dad."

Neil, 53, shares Harper and Gideon with his husband of 12 years, David Burtka, 51. The couple welcomed their children via surrogate in October 2010.

In the sweet birthday tribute, little Harper wore a pink tutu and held a fuzzy pink crown, while her twin Gideon smiled with a bib around his neck. In the more recent photos, Harper posed for a black-and-white portrait, while Gideon sat on a boat wearing sunglasses.

Friends and fans of the family flooded the comments of Neil's post to share their reaction to the famous twins being all grown up.

Actor Jonathan Tucker wrote: "Too. Fast." Queer Eye for the Straight Guy star Carson Kressley added three clapping emojis. And fans of the couple shared a shocked sentiment that the twins are 16.

"16 already? Gosh I remember when you were setting up the nursery! Happy birthday Harper & Gideon!" one fan wrote. Another commented: "Happy 16th to the babies. It's incredible how fast time goes. Well done, dads. They look like wonderful humans."

What Neil Patrick Harris' children really think of him

While the actor has won both an Emmy and a Tony award, his children just think of him as dad. During a recent appearance on Today with Jenna & Sheinelle, Neil got candid about what the twins think about his career.

Sheinelle Jones was positive that his twins were highly impressed by his career, stating: "They know how cool you are, obviously, at this point."

Contrary to Sheinelle's take, Neil confessed: "Oh, I don't think they think I'm cool at all. I'm one of their fathers."

Regardless of what Harper and Gideon think of their dad, Neil is proud of his kids. "My son Gideon now, is going to a professional performing arts school, here in New York. So he wants to be an actor as well," he told Jenna Bush Hager, continuing: "They're just amazing human beings. I think the world of them."

The actor went on: "I wasn't emotional when they were little kids because there was so much time that they could grow, but now that they're in high school, I just watch them with so much pride."