Rory McIlroy filed for divorce from wife Erica Stoll on Tuesday, with the couple splitting after seven years of marriage.
And sources say the bombshell 'came out of the blue', with McIlroy previously showing no sign there was anything happening behind the scenes.
McIlroy filed divorce documents on Tuesday, having previously started dating Stoll following his split from tennis star Caroline Wozniacki in 2014.
He had met Stoll two years previously at the Ryder Cup, with Stoll working as a PGA transport official at the time.
Rory McIlroy and Erica Stoll are divorcing after seven years of marriage
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McIlroy's form has recently improved, with the golf star winning the Wells Fargo Championship over the weekend.
While celebrating that triumph, the Northern-Irishman had his wedding ring on.
Yet a source has told The Sun that the split has 'come out of the blue', with the insider saying 'no one saw it coming'.
They're quoted as saying: "Their split comes right out of the blue and no one saw it coming.
"The timing is very odd with Rory about to take part in a tournament but perhaps he wanted to get things tied up before it started.
"Ironically, Rory is in some of the best form of his life so whatever has been going on behind the scenes has not affected him at all."
McIlroy seemed at ease as he took to the green at Valhalla Golf Club for practice on Tuesday.
He is currently preparing for the start of the PGA Championship, with that tournament commencing on Thursday.
McIlroy looked happy and relaxed as he practiced alongside caddy Harry Diamond in Louisville, Kentucky.
Diamond was previously McIlroy's best man when he married Stoll in 2017.
McIlroy and Stoll have a three-year-old daughter named Poppy.
The divorce filing revealed the couple had a pre-nuptial agreement, with their relationship also 'irretrievably broken'.
The divorce filing also asked for split custody of Poppy, too.
McIlroy hasn't won a major in his last 10 attempts but, after winning the Wells Fargo Championship, is now back in form once again.
And he insisted over the weekend that he's a better player than he used to be, despite his inconsistent form.
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Rory McIlroy and Erica Stoll married back in 2017
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“I've been sort of banging this drum for the last few years, but I'm a way better player now than I was back then," he said over the weekend.
"I haven't had the major record to back that up, but I've had the wins, I've done everything else there is to do in the game since 2014.
“The only thing I need to do is get another major.
"You know, a win like this going into the PGA Championship next week is a good way to prep for that.”
Meanwhile, former major champion Rich Beem thinks Scottie Scheffler is the only man capable of beating McIlroy later this week.
Rory McIlroy is currently preparing for the PGA Championship later this week
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"If McIlroy impresses with the driver again, then I don't see any reason in the world - other than a certain Scottie Scheffler - why he can't win this week," he told Sky Sports.
"Scheffler has been in brilliant form, but it will be interesting how much the birth of his son has impacted his prep going into this week."