PGA Tour players were kept in the dark over the merger and are said to be furious.
In a 'heated' players meeting with Monahan this afternoon, calls for his to stand down were met with a standing ovation.
More below.
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PGA Tour and LIV Golf merger LIVE: Latest updates following bombshell announcement
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Follow Mail Sport's live blog for all the updates following the shock news that the PGA Tour is merging with its Saudi-backed rival, LIV Golf.
Monahan's job could be on the line
Monahan revealed in a press conference that the merger had been in the works for seven weeks, but the stars of the PGA Tour were left in the dark, forced to find out in real time on social media.
Mail Sport's Oliver Holt gives his take on today's announcement
Mail Sport's Oliver Holt has hit out at today's decision to merge the PGA Tour and LIV Golf.
Read what Holt has said by clicking on the link below...
OLIVER HOLT: It's about the money, stupid. It's always about the money. It's about empty words, too. The empty words spoken by hollow men like Jay Monahan, the PGA Tour commissioner.
Koepka slams LIV Golf critic
Five-time major winner Brooks Koepka joined LIV Golf last year, and has regularly received criticism from analyst Brandel Chamblee since.
Following's today's shock announcement, he has now joked on twitter that someone should do a 'welfare check' on Chamblee.
Chamblee, who's a former PGA Tour pro, has been one of Koepka's biggest critics and has previously criticised Saudi Arabia's foreign investment fund, also known as PIF, for backing LIV Golf.
How much did LIV rebels pocket?
Rory McIlroy and Tiger Woods both resisted the temptation to join LIV Golf last year, but others were more than happy to go.
Mail Sport has taken a look at exactly how much they have pocketed from the series over the last 12 months...
The deal will end the acrimonious split in the sport and pending litigation between the two tours will be stopped. They will proceed as part of the same enterprise.
How LIV won golf's civil war...
It has been an ugly battle over the past 12 months, but LIV Golf have got their way in the end.
Mail Sport looks at how they came out on top following today's announcement.
READ MORE BELOW...
In the bitter civil war between the tradition-steeped PGA Tour and its filthy-rich, Saudi-backed rival LIV Golf over the future of golf, the money has come out on top.
What happens following the merger?
There are so many questions that need answering after today's shock announcement.
Mail Sport has done our best to break down exactly what golf could look like moving forward by answering all the pressing questions.
READ MORE BELOW...
News broke earlier today that the PGA Tour and DP World Tour are merging with Saudi-backed LIV Golf to form 'a new collectively owned' entity.
PGA commissioner hails 'momentous day'
It's hard to imagine that McIlroy is particularly thrilled with today's announcement, but PGA commissioner Jay Monahan seems to be.
He has written a letter to Tour members following the news, insisting players will 'benefit for years to come' from the merger.
READ MORE BELOW...
PGA commissioner Jay Monahan has hailed a 'momentous day' for the sport in a letter to Tour members to reveal their decision to merge with rivals LIV Golf.
McIlroy mocked by fans online
McIlroy has been adamant that he would not be joining LIV Golf over the past year, but he will now have to work with the organisation following the merger.
Fans have been poking fun at his decision to turn down $500m to stay loyal to the PGA Tour.
READ MORE BELOW...
The PGA was accused of violating antitrust laws by banning LIV players from its tour, golf's preeminent circuit countersued its Saudi-backed rivals, accusing the outfit of interfering with its deals.
How will the players take the news?
This is an issue that has divided golf for over a year.
The likes of Mickelson, Sergio Garcia, Lee Westwood and Ian Poulter have all defended their decision to join LIV Golf, while Rory McIlroy has been particularly critical of those who chose to walk away from the PGA Tour.
In the last couple of days, Mickelson even hit out at McIlroy, claiming he'd be 'perfect' for LIV Golf, but accused him of coming out with too much 'BS'.
Now the pair are set to be back on the same tour!
Phil Mickelson has continued his ugly war of words with Rory McIlroy and the PGA Tour - claiming that 'no LIV Golf team would want the former world No 1' because of 'all his BS'.
Phil Mickelson reacts...
Six-time major winner Phil Mickelson has been arguably the highest-profile name involved with LIV Golf since its inception.
He has been unable to hide his delight with the decision for LIV Golf to merge with the PGA Tour after repeatedly defending the former over the past 12 months.
After news spread that the PGA Tour and LIV Golf were merging, social media reaction was swift from golfers on both sides of the fight.
Only one place to start...
Let's begin with what has happened.
Just over an hour ago it was announced the PGA Tour and LIV Golf will be merging to form a new commercial entity.
READ BELOW FOR THE FULL STORY...
The PGA Tour is reportedly merging with its Saudi-backed rival, LIV Golf. The two separate entities would combine to form a new yet-to-be-named company, ending their brief, bitter feud.
Good afternoon!
Well who saw this coming?
It has been officially confirmed that the PGA Tour and the Saudi-backed LIV Golf will be merging after months of back and forth between the two organisations.
Mail Sport will be bringing you all the latest reaction to the bombshell announcement as we get it.
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