When Mike Tirico left ESPN for what was seemingly a lesser role at NBC, sports fans wondered why.

Now we know.

On Thursday, NBC announced that Tirico will be taking over as the lead prime time Olympics announcer starting with the 2018 Winter Games.

Mark Lazarus, NBC Chairman of Broadcasting and Sports, talked about Costas’ contributions and the transition in a press release by the network.

“For a quarter-century, Bob expertly piloted NBC’s prime time coverage of the Olympics,” Lazarus said. “It is with a tremendous amount of pride that I can simultaneously express our appreciation for Bob’s stellar, record-setting run, while also feeling very lucky that we have someone as talented as Mike to take over as our new prime time host.”

Costas explained why he’s stepping aside now.

“It has been both a privilege and an incredible personal and professional experience to have been part of NBC’s Olympic coverage all these years,” said Costas, who has the longest tenure of NBC’s sports announcers (37 years).

“I’m especially appreciative of all the talented and dedicated people I worked for and with on those broadcasts. I always felt that, in a certain sense, I was carrying the ball for them. It’s been a wonderful run, but I just felt now was the right time to step away and I’m grateful that NBC left that decision to me.”

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Tirico thanked his predecessor and the network.

“The level and longevity of Bob’s tenure have left an indelible mark on American television and the Olympic Games,” said Tirico. “I am honored to call him a friend, humbled by this opportunity, and thankful to the many people who have helped make this possible.”

The 2018 Winter Games will take place in PyeongChang, South Korea next February.

Joe Giglio may be reached at jgiglio@njadvancemedia.com. Follow him on Twitter @JoeGiglioSports. Find NJ.com on Facebook.

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