Tag Heuer is to bring to an end its 30-year association with McLaren come the end of the current Formula 1 season and switch to rival Red Bull.
The brand has featured on the team's cars since 1985, with former Tag Heuer CEO Mansour Ojjeh having initially become involved in McLaren two years earlier.
In a major coup, the iconic watch brand has decided to join forces with Red Bull from next season, drawing into question that team's partnership with Casio.
In a recent interview with Swiss magazine L'Hebdo, current Tag Heuer CEO Jean-Claude Bivet said: "We have just signed Red Bull Racing in F1 for next season.
"It is a young, dynamic, go-getter, perfectly consistent with the TAG Heuer strategy."
McLaren has also confirmed the split, with a spokesman stating: "McLaren's partnership with Tag Heuer has been one of the most successful and enduring sponsorships in sporting history.
"It has lasted 30 years, during which time both parties have achieved enormous success together.
"On track the team has won grands prix and world championships with such iconic racing heroes as Alain Prost, Ayrton Senna, Mika Hakkinen and Lewis Hamilton.
"Off track Tag Heuer's association with the team has caused its watches to become globally synonymous with high technology, precision and speed - three principal hallmarks of the McLaren brand.
"It is therefore with gratitude we announce the end of our 30-year partnership, satisfied as both parties are with a job well done.
"Our relationship with Tag Heuer's parent company LVMH continues via our new partnership with Chandon, announced last month."
The loss of Tag Heuer is the latest sponsorship blow to McLaren as the team has been without a primary sponsor since Vodafone departed at the end of 2013.
Hugo Boss, having been with McLaren for 33 years, has also departed in recent times, while Santander has significantly downscaled its involvement.