WATCH: Surprise Celtics Guest at Patriots Practice

Monday's practice for the New England Patriots featured heavy rain, some standout performances and an appearance by one of Boston's other proud sports franchises.

The Patriots welcomed Boston Celtics coach Joe Mazzulla to observe their training camp practice. The Celtics coach had a chance to learn from the best, as NBC Sports Boston captured him having a lengthy conversation with Patriots coach Bill Belichick.

The rain didn't stop #Celtics HC Joe Mazzulla from having a lengthy talk with Belichick at Pats camp today!

Would love to be a fly on the wall during this conversation 👀 #ForeverNE #BleedGreen pic.twitter.com/FoD86nbedY
— Patriots Coverage on NBCS Boston (@NBCSPatriots) August 7, 2023

Mazzulla took the reins for the Celtics last season, initially on an interim basis before officially becoming the permanent coach in February. He led the Celtics to a 57-25 record, but the season ended with a Game 7 loss to the Miami Heat in the Eastern Conference Finals. Mazzulla finished third in NBA Coach of the Year voting.

This isn't the first time Belichick has parted some advice on another Boston coach. In April, Boston Bruins coach Jim Montgomery, who guided the B's to the best regular season in NHL history in his first year at the helm, revealed that Belichick had been guiding him throughout the season.

"I've been able to talk with Joe Mazzulla and (we) text every once in a while, more congratulating each other on the seasons we're having," Montgomery told NBC Sports Boston. "And then I had the opportunity when I went to a Patriots game to meet the legend, Bill Belichick.

"He gave me some really good advice on when the team is going really well and when they're not; when to push, when to pull away. That was really insightful."

If coaches want to learn how to win, Belichick is just about the best person to ask. He has nearly 30 years of head coaching experience under his belt, and led the Patriots to six Super Bowl championships over the span of two decades. Even as the legendary coach may be nearing the end of his storied career, his legacy speaks for itself.

Boston had gained a reputation as one of the best sports cities in the U.S., with each of its four major teams winning championships somewhat recently. This season, the Patriots, who spearheaded Boston's rise with their 20-year dynasty, and the other teams will look to prove that's still the case.

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