The first Patriots free agent is off the board.

Offensive tackle Trent Brown intends to sign with the Raiders when the new league year begins on Wednesday, a source confirmed.

ESPN’s Adam Schefter reported the deal will be worth $66 million over four years with $36.75 million guaranteed.

The contract makes him the highest paid offensive lineman in NFL history.

Brown’s departure is no surprise. The expectation all along was that he’d leave New England following a strong 2018 campaign as the team’s left tackle.

The 6-foot-8, 380-pound Brown was acquired by the Patriots in a trade with the 49ers a year ago. New England flipped a third-round pick (No. 95) for Brown and a fifth-round selection (No. 143, which was used to select linebacker Ja’Whaun Bentley). The Pats received a year of terrific production from Brown, and they’re now likely to recoup a 2020 compensatory pick following his departure to Oakland.

An exceptional athlete for his size, Brown was stellar in pass protection and helped anchor one of the league’s better rushing attacks.

Second-year pro Isaiah Wynn likely slides in as the Patriots’ starting left tackle. Wynn suffered a season-ending Achilles injury during the preseason. He was New England’s top selection in the 2018 NFL Draft.

The club’s No. 3 tackle, LaAdrian Waddle, is a free agent.

Even though the Patriots selected Wynn a year ago, they could prioritize offensive tackle again in April’s draft. They hold six picks in the top three rounds.

The Pats have several other marquee free agents, none more important than defensive end Trey Flowers. As many other free-agent defensive ends have been given the franchise tag, Flowers’ value on the open market has only increased over the past week.

Dallas’ DeMarcus Lawrence, Houston’s Jadeveon Clowney, Seattle’s Frank Clark, and Kansas City’s Dee Ford were all retained via the franchise tag. Flowers heads into free agency as the top edge defender on the board. He’ll be expensive for the Patriots to re-sign.

Patriots receivers Phillip Dorsett, Chris Hogan, and Cordarrelle Patterson are also free agents.

The team is expecting significant turnover at the position.