Josh Radnor Marks How I Met Your Mother's 18th Anniversary with Fun Cast Throwback: 'Look at Those Babies!'

'How I Met Your Mother' made its CBS debut on September 2005 and ended in March 2014 after nine seasons

Josh Radnor is celebrating a major milestone for How I Met Your Mother!

As the CBS hit marked the 18th anniversary of its premiere on Tuesday, Radnor commemorated the occasion by sharing a throwback photo of the cast during the show's debut season.

"Look at those babies!" wrote the Fleishman Is in Trouble actor, 49. "Apparently 'How I Met Your Mother' premiered eighteen years ago (yesterday, I think)!!! How is that possible?? I am immensely grateful to have been part of a show that continues to mean so much to so many people. It's hard to fully appreciate something like that in the moment but all these years later I got nothing but love for that show and the people I made it with."

Radnor added, "Thanks to everyone for continuing to watch it and quote it and remind me of the hilarity and depth of what we created. Means a lot. And Happy 18th HIMYM!!"

Related: The Cast of 'How I Met Your Mother' : Where Are They Now?

How I Met Your Mother ran on CBS from September 2005 to March 2014 for nine seasons. Radnor starred alongside Cobie Smulders, Neil Patrick Harris, Alyson Hannigan and Jason Segel. The series was narrated by Bob Saget and eventually featured Cristin Milioti as the titular mother.

The Emmy-winning sitcom followed Radnor's character Ted Mosby as he tells the story of meeting the mother of his children in reverse.

Following the show's successful run, a spinoff titled How I Met Your Dad — featuring Barbie director Greta Gerwig in the lead role — was greenlit. However, it was later canceled after filming on the pilot concluded due to poor reception.

A second spinoff starring Hilary Duff, titled How I Met Your Father, was later picked up by Hulu. It was recently canceled after two seasons.

Related: Josh Radnor Has Mini 'HIMYM' Reunion with Alyson Hannigan: 'Love This Gal Forever'

After all these years, How I Met Your Mother has still remained popular among audiences who have either newly discovered the series or begun rewatching it amid the digital streaming age. But the series finale has still proven to be divisive for fans old and new, because of the controversial decision to kill off Milioti's titular character in the final moments.

Coming to the episode's defense, Radnor told Time Magazine, "I think that a lot of people who stuck with the series from day one really got it."

"I think the series and the finale are going to age pretty well, that's my sense," he said. "Various arts are littered with stories of things being greeted with outrage that go on to find their place and be looked on in a different way. I think some of that outrage spoke to how passionately people felt about it."

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All nine seasons of How I Met Your Mother are available to stream on Hulu.

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