NEW YORK — The New York Mets said nighty-night to the Dark Knight.

Matt Harvey, once regarded as a premier pitcher who could have joined Tom Seaver and Dwight Gooden among the Mets’ greats, refused a minor league assignment and will be designated for assignment Saturday.

The 29-year-old right-hander lost his spot in the rotation last month after four starts, and he had a 10.50 ERA in four relief appearances.

“It’s the end of an era,” Mets general manager Sandy Alderson said before Friday night’s game against Colorado. “And I used that term in broad senses. Matt has been a cornerstone certainly of my tenure here, a tremendous prospect at the time I arrived, tremendous accomplishments during the course of my tenure here. And it’s a very unfortunate, difficult conclusion.”

New York had hoped Harvey would be willing to work at the team’s minor league complex in Florida in an effort to regain form. Harvey refused.

“We feel Matt is a starter (and) needs to work on 4 pitches,” his agent, Scott Boras said in a text message. “In the bullpen a pitcher tends to focus on 2 pitches.”

After Harvey is designated, the Mets have seven days to trade or release him.