Phil Mickelson has ended his 25-year partnership with caddie Jim Mackay.
Mickelson won five majors and 41 PGA Tour titles with Mackay - nicknamed 'Bones' - on his bag.
The 47-year-old said the separation was "mutual" and confirmed his brother, Tim, will take over from Mackay.
"Our decision is not based on a single incident. We just feel it's the right time for change. Bones is one of the most knowledgeable and dedicated caddies in the world," said Mickelson.
"The next player to work with him will obviously be very lucky. My relationship and history with Bones far exceeds golf. He has been one of the most important and special people in my life since the day we met, and I will always be grateful for everything he has done for me."
Mickelson has earned in excess of $80m (£63m) in prize money since working with Mackay. He has won the Masters three times, the Open Championship and the US PGA, as well as finishing second or tied for second six times at golf's other major, the US Open.
Mackay was at Erin Hills last week to prepare for the US Open in the event Mickelson was able to take part in the tournament, which clashed with his daughter's graduation ceremony.
In a statement Mackay said: "When Phil hired me in 1992, I had one dream: to caddie in a Ryder Cup. Last year, at Hazeltine, Phil played in his 11th straight Ryder Cup. It was so cool to have a front-row seat.
"I wish Phil nothing but the best. His game is still at an elite level, and when he wins in the future (definitely the Masters), I will be among the first to congratulate him."