Harris, 40, starred as the legendary Barney Stintson in the CBS sitcom, which came to a close on March 31 after nine seasons. In the two-hour finale it is revealed that The Mother (played by Tracy McConnell) had been dead all along and that Josh Radnor's Ted Mosby ends up with his on-and-off flame Cobie Smulder's Robin Scherbatsky after her character gets a divorce from Stintson's.
"It wasn't necessarily the happy ending people were expecting," Harris told Letterman. "But Carter and Craig, who were once writers on your show and the executive producers and the creators, knew this ending years ago and had played towards that. I was a big proponent of it and a big fan of it."
"Sometimes people's growth doesn't really mean that they grow up. There are certain people who you want to get in a solid relationship and really settle down and learn from things. You want Barney to be the guy you can bring your mom home to, but Barney's the guy who wants to bang your mom. At the end of the day, it's not always meant to be that way."
Following the predominately-negative backlash that ensued after the show's final episode aired, series co-creator and executive producer Carter Bays took to Twitter to announce that while he stood by the ending, the team chose an alternate ending to be included in the complete series DVD set, which will go on sale in the fall.