Who said rivals couldn’t make trades?

The Yankees are sending reliever Adam Ottavino and a prospect to the Red Sox in a surprising trade, The Post’s Joel Sherman confirmed on Monday. The Athletic first reported Ottavino was headed to the Yankees’ rival.

Ottavino has one year left on his contract at $9 million, with the Red Sox expected to take on most of the money. The right-handed reliever had an off year last season, posting a 5.89 ERA in the shortened campaign after recording a much sharper 1.90 ERA in his first season in the Bronx.

While Ottavino is a Brooklyn product, he’s no stranger to Boston, after playing college baseball at Northeastern.

“I want to stay on the team. I want to prove my worth. I want to pitch well,” Ottavino told The Post’s Ken Davidoff in December. “I want to finish what we tried to start these last few years and win that title and all that. It’s not up to me. So I don’t pay attention to any of that, really.”