FOXBORO — Buddy is back.

Veteran linebacker Junior Seau — known to his teammates in the Patriots locker room as “Buddy” — officially returned to New England on Wednesday, signing a one-year deal with the Patriots.

The 40-year old Seau has played parts of the last three seasons for New England. In recent months, he’s talked about possibly returning to pro football, but told people the only team he would return to play for would be the Patriots. He explained why Wednesday afternoon.

“I know the system. I trust the coach and the ownership and the coaches in this organization, and I have a lot of love for the players in that locker room,” Seau said. “That’s the reason I wanted to come back to only one team.

“And I trust this coach, Bill Belichick.”

“It’s good to have Junior back,” Belichick said. “We’re glad to have him.

“He’s a pretty special guy, I think we all know that," Belichick added. “Physically, his make-up, his instincts, he’s just a football player, and a real good one. He’s a Hall of Fame guy. There’s not too many of those coming down the pike.”

“He looks great,” said quarterback Tom Brady. “He looks like he’s 25.”

That energy and enthusiasm that was Seau’s trademark for the last 19 seasons was still there — according to Brady, Seau was in the weight room working up a sweat when the quarterback arrived for work at 6:45 on Wednesday morning.

“Everyone asks ‘Are you eager? Are you excited?’ I’m too old to be excited,” Seau said with a laugh. “Can I say that? I am. I’m too old to jump up for joy.

“I’m not going to blow out the cake and jump around. This isn’t the time to do that,” he added. “This is the time to go to work. Gimme a helmet and let’s build the player that I can be this year. That’s all I ask.”

A 12-time Pro Bowler, Seau has 1,515 tackles, 17 fumble recoveries, 18 interceptions, and 56½ sacks in a 19-year NFL career that’s included stops in San Diego, Miami and New England.

After a little uncertainty involving his old No. 55 this time around — he initially said he would “take a couple of dinners” to wrest it away from fellow linebacker Derrick Burgess — he was back in his old number by the time practice rolled around Wednesday afternoon. (Burgess switched to No. 53.)

He isn’t sure if he will be asked to suit up this week — Seau said, “Whatever Bill needs” when asked if he’ll be ready to go this Sunday against Tennessee — but will likely provide depth at the inside linebacker position when New England is in the 3-4. In addition, Belichick hinted that Seau’s versatility may allow him to see some time outside when the Patriots are in a 4-3.

“Bill doesn’t kick around tires and say ‘I’m just going to go grab a guy that’s 40-years old off the surfboard and say come and join us.’ He has a plan,” Seau said. “And his plan is something that we’re going to try and implement, whatever it may be. He knows who I am and I know what he has to offer. I trust Bill.”

With the recent departures of veterans like Tedy Bruschi, Mike Vrabel, Rodney Harrison and Richard Seymour, Seau brings a dose of veteran leadership to a defense that has gotten much younger since the last time he donned a Patriots uniform.

Among those youngsters eager to learn from Seau is safety Pat Chung. The 22-year-old rookie is the youngest player on the active roster — wide receiver/returner Brandon Tate is 2 months younger — and Chung was 3 years old when Seau entered the league in 1990.

“How much more experience can you get from somebody?” said Chung. “He’s been doing it for years now. Now I know if I have a question, I’m going right to him. I’ve only talked to him since he’s been here for like a couple of seconds, and he’s smart and down to earth, and he seems like he’s ready to help us. No complaints here.”

“There’s a linebacking corps that we have now that was probably in first grade when I was a rookie,” Seau said. “So there’s a lot of youth, but they can play the game.

“If there’s anything I can do to help them either in the meeting room or the weight room, whatever it may take, it’s gong to be fun playing with them. But they’re definitely young.”