Two-time NBA all-star swingman Jaylen Brown has agreed to a five-year, $304 million supermax contract extension with the Boston Celtics, his agent Jason Glushon told ESPN.

The deal is the richest in NBA history, eclipsing the $276 million contract of Denver's Nicola Jokić, signed in 2022, according to salary tracking website Spotrac.

CNN has reached out to Glushon and the Celtics for comment.

Citing sources, Shams Charania of The Athletic and Stadium tweeted that the contract is fully guaranteed.

Last season, Brown, a guard/forward, averaged a career-best 26.6 points, 6.9 rebounds and 3.5 assists per game.

The 26-year-old was named to the 2022-23 All-NBA second team. Brown, the 2016 No. 3 overall pick, was eligible for the new contract as a result of making the All-NBA team.

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In seven seasons in Boston, Brown has helped the Celtics advance to five Eastern Conference Finals and an NBA Finals appearance in 2022.

ESPN reported the contract extension begins in the 2024-2025 season and runs through the 2028-2029 season, when Brown will be 32.

His previous contract was a four-year, $106 million deal, according to Spotrac.