NASCAR points leader Matt Kenseth, one of the longest-tenured drivers in the series, is leaving Roush Fenway Racing at the end of the season.

He will be replaced in the No. 17 Ford — the car he has driven for all but one of his 452 career starts — by Nationwide Series champion Ricky Stenhouse Jr. and Kenseth's long relationship with Ford will apparently come to an end. He is believed to be headed to Joe Gibbs Racing, either in Joey Logano's No. 20 Toyota or a fourth unannounced team.

Why? Good question. The team offered no answers in the sudden divorce of one of NASCAR's longest active relationships. Only Jeff Gordon, with Hendrick Motorsports since 1993, has been with his team longer than Kenseth has been with Jack Roush.

"I'd like to thank Matt Kenseth for his many years of loyal service," co-owner Roush said Tuesday. "Matt has been an integral part of this organization for well over a decade, and we are extremely appreciative of his accomplishments and contributions to the team, and will always consider him a part of the Roush Fenway family."

Kenseth and teammate Greg Biffle are ranked 1st and 2nd in the Sprint Cup Series, clearly poised to make a run at the championship. Kenseth opened the season with his second Daytona 500 victory, and has 11 top-10 finishes through 16 races.

Kenseth did not respond to a request for comment on Tuesday, but tweeted about his departure.

"I'm very thankful to Jack Roush for the opportunities he's given me over the past 14 years. Together we have enjoyed a lot of success," he posted. "And as a team we are committed as ever to the remainder of the 2012 season and chasing a 3rd sprint cup title for Jack and RFR."

With Roush, Kenseth has built a career worthy of Hall of Fame consideration. Besides the wins at Daytona, he has won 22 Cup races overall, and the 2003 championship. In the Nationwide Series, Kenseth has won 26 races driving for Roush.

His relationship with current general manager Robbie Reiser, like Kenseth a native of Wisconsin, dates at least to 1997, when Kenseth first drove Reiser's No. 17 entry. It was eventually merged into the Roush organization, and Reiser became Kenseth's crew chief at Roush in 2000, Kenseth's rookie season.

"Matt and I broke into this sport together, learned the ropes and were able to bring home a championship," Reiser said. "Over the 20 years we have worked with each other, Matt has been a fierce competitor and become a close friend, not only for me, but as a mentor to young drivers like Ricky. I wish Matt nothing but the best for the next phase of his career, and know that we'll remain close."

There was speculation last weekend at Sonoma that Kenseth was leaving to join JGR, which is in a contract year with Logano. The team also has room to expand to a fourth car, and it is possible Gibbs officials are trying to move Kenseth in and keep Logano at the same time.

Team president J.D. Gibbs did not respond to a request for a comment Tuesday, and said at Sonoma he could not talk about Kenseth.

Jamie Allison, director of Ford Racing, said the blue oval brand is was disappointed Kenseth is leaving.

"He will be certainly missed by us and the Ford Racing fans," Allison said. "We are thankful for Matt's winning efforts and championship-caliber success with the Roush and Ford racing programs these past 16 years, both on and off the track. We will focus on this year and look forward to more success on the track in his No. 17 Ford Fusion this season."

Kenseth's car has had sponsorship woes the last few years, and Roush is funding a large portion of this year's schedule himself for the 40-year-old Kenseth. The organization dropped David Ragan and its fourth team because of a lack of sponsorship at the end of last season, and also ponied up significant money to re-sign Carl Edwards last season. Roush also signed Biffle to a contract extension last season.

The team desperately needs a slot for the 24-year-old Stenhouse, who is locked into a long-term contract but has nowhere to go in Roush's Cup lineup. The organization has a similar problem with 2011 Daytona 500 winner Trevor Bayne, who is also in a long-term contract and had his Nationwide Series team shuttered earlier this season because of no funding.

Stenhouse will be far cheaper than Kenseth in terms of salary, and he is much younger and clearly has a future with the organization.

"We feel that he is not only a key piece of our team's future, but a key piece of the future of the sport," Roush said of Stenhouse. "Roush Fenway is an organization with a wonderful past and present, as well as an extremely promising future, and I can't think of a better candidate than Ricky to usher in the next era of success for the team."

It's unusual, though, for a team and driver to decide to part ways during a championship run. Roush technically has three shots at the Sprint Cup title, as Biffle has proven to be just as strong as Kenseth this season. And Edwards, who tied Tony Stewart last year for the championship but lost the title on a tie-breaker, could still qualify for the 12-driver Chase for the Sprint Cup championship field.

Roush, meanwhile, doesn't think Kenseth's departure will hurt the No. 17 team's championship hopes.

"The No. 17 is positioned extremely well this season, and I'm committed to providing the team the best resources to continue their run for the 2012 championship," he said. "I have no doubt that Matt will do his part."