Jurgen Klopp, who has often waxed lyrical about the South Korean, identified the Spurs star as a potential replacement for Sadio Mane.
Liverpool were prepared to test the north Londoners' resolve with a substantial bid for Son had they not finished in the top four, report Football.London.
Considering that the 29-year-old finished joint top goalscorer last season and that Tottenham spent all of last summer fending off interest in Harry Kane, it would have undone a lot of the progress made under Antonio Conte for Liverpool to pinch Son.
Yet it still would not have been the most controversial transfer between two of the Premier League's 'big-six' - that honour falls to one of these…
Carlos Tevez (Manchester United to Manchester City)
Tevez was very popular at Man United during a successful two-year loan spell where he won the Champions League in 2008, with fans regularly chanting: 'Fergie, sign him up'.
A year later, though, he was a Man City player - the first to move directly to the club since 1999 - and City supporters carried on the chant just to rub it in.
The club, meanwhile, celebrated the deal publicly with a huge billboard reading: 'Welcome to Manchester'.
Sir Alex Ferguson wasn't impressed - 'a small club with a small mentality', he said at the time.
Sol Campbell (Tottenham to Arsenal)
The former England defender spent more than 12 years at Spurs, rising through the youth ranks and going on to be a star for their first team.
After 315 appearances, he rejected the offer of a new contract and made the hugely controversial move across north London on a free transfer.
His decision to join Arsenal infuriated Tottenham fans, with Campbell branded 'Judas' and subjected to sickening chants and death threats.
Campbell went on to become part of the 'Invincibles' side that won the Premier League title at White Hart Lane and, to this day, remains a figure of hate at Tottenham - though the man himself told talkSPORT last year that it's time to 'move on'.
Emmanuel Adebayor (Arsenal to Manchester City)
The Togo striker infamously admitted that he still 'hated' Arsenal in 2018 - nine years after his controversial exit from the club.
Adebayor made his feelings towards his former side clear in his maiden campaign at the Etihad, running the length of the pitch to celebrate in front of the Arsenal fans after scoring in a 4-2 win.
"I was being abused by people who six months ago were singing my name and the abuse was for no reason," he said. "There is only so much abuse a man can take until he reaches breaking point."
"I scored and I wanted to show people it is not a good idea to abuse me. I really don't understand it at all," Adebayor added.
"They were clapping [former Arsenal defender Kolo Toure] but they were shouting abuse at me before the match even kicked off."
Fernando Torres (Liverpool to Chelsea)
'There aren't many people who can break your heart, yet you still love them' - was a Reds fans tribute to El Nino after he retired in 2019.
Part of the recent good feeling towards Torres from Anfield might be that he never recaptured his form in London following his £50m move.
He scored 81 goals in a Reds shirt, to only 45 for the Blues - though to be fair one of those was that famous strike against Barcelona…
And trophies are how a lot of players are judged at the end of their careers and despite his injury troubles, Torres still went on to lift the Champions League, Europa League and FA Cup for Chelsea.
Kyle Walker (Tottenham to Manchester City)
Walker recently admitted he rang his dad and questioned if leaving Spurs was a 'mistake' during his first pre-season with City.
While the four Premier League titles he's won since has proven it wasn't, doubts are still present over whose choice it actually was for him to leave.
Then-Spurs manager Mauricio Pochettino wrote in his book that the club were forced to sell after Walker showed an 'alarming lack of respect to his team-mates' by asking to leave at the end of the 2016/17 season.
The England defender disputes this and claimed that he only sought pastures new after Pochettino began to exile him from the team.
He told the Daily Mail: "I have had a few people calling me a snake and stuff.
"It hurts because I gave everything to that club. And everything I am now I owe to that club. So yes, it hurts when I go back there now, but I guess it's just a part of football."
Ashley Cole (Arsenal to Chelsea)
'Probably some of you think I'm a greedy pig, and it's nothing like that' was the quote from Cole after arriving at Stamford Bridge in 2006.
Yet it did little to stop Arsenal fans dubbing him 'Cashley' following his move to the club's London rivals in 2006 in a £5million deal that saw William Gallas head the other way.
Cole was an integral part of two Premier League title wins with his boyhood club, but joined Chelsea a year after allegations of tapping up saw him and Jose Mourinho each fined £75,000.
Arsenal then waited eight years for a trophy after the left-back's departure while Cole enjoyed a silverware-laden spell at the Blues.
Petr Cech (Chelsea to Arsenal)
The Czech Republic icon was a stalwart at Stamford Bridge but Thibaut Courtois' return relegated him to the bench.
Cech earned the blessing of Roman Abramovich to remain in London and seal a £10m move to the club's rivals Arsenal.
Yet Jose Mourinho was overruled in selling to a direct rival while then-Blues midfielder Nemanja Matic admitted he wasn't happy with the move either.
Cech himself was branded a traitor and said: "There are some people who have left me negative messages, but they aren't true Chelsea fans."
And, despite John Terry suggesting Cech would win Arsenal 12 to 15 points a season, the Gunners dropped out of the top four in the keeper's second campaign.
Raheem Sterling (Liverpool to Manchester City)
The England star went from hero to villain on Merseyside when he forced his way out of the club in 2015, making a £49million move to City.
Just months earlier Sterling had angered Liverpool fans by giving an unauthorised interview where he didn't want to be perceived as a 'money-grabbing 20-year-old'.
"I don't regret doing the interview because it was frustrating hearing some of the stories about myself and some of the silly money people said I was supposedly rejecting, when it was nothing like that," Sterling said later.
"I just wanted to get my point across but probably there was a better way I could have done it."
Sterling, who has racked up ten trophies at the Etihad, has been subjected to plenty of abuse on his returns to Anfield but insisted in 2020 that that has not diminished the love he has for Liverpool.
Robin van Persie (Arsenal to Manchester United)
The Dutchman's move to Old Trafford from Arsenal caused shock waves around the world in 2012.
With just one year left on his contract at the Emirates, Van Persie announced he would not be penning fresh terms and subsequently joined United in a cut-price £24m deal.
The striker enjoyed a sensational debut campaign with the Red Devils, scoring 26 goals to fire United to a record 20th league title.
RVP said upon signing for United: "I always listen to the little boy inside of me in these situations - when you have to make the harder decisions in life. What does he want? That boy was screaming for Man United."
Alexis Sanchez (Arsenal to Manchester United)
Sanchez knew he made a mistake following in Van Persie's footsteps by moving to the Red Devils… after just a single training session.
The Chilean headed to Old Trafford in a highly-anticipated January 2018 transfer, with United reportedly paying him around £560,000-a-week.
But his time in Manchester was an unmitigated disaster, as he scored just five goals in 45 games before he was shipped out to Inter Milan.