Despite spending seven years at Stamford Bridge and having a senior appearance under his belt, the youngster has fallen down the pecking order in west London and Spurs are set to pinch the talented teenager.
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The centre-forward - who was also wanted by Manchester City - is highly rated in the Blues' academy, but is now in the final six months of his contract.
And Spurs appear to have won the race for him, offering him a 'long-term pathway to the first team via loans from next season', much like they have for young striker Dane Scarlett, who's on loan at Portsmouth.
Born in Chippenham, Wiltshire, Soonsup-Bell came through Swindon Town's academy as a midfielder.
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However, after just three years at the County Ground, he was snapped up by Chelsea at the age of 12 after being scouted by Blues scout and England star Tyrone Mings' dad, Adie.
So what's Soonsup-Bell's story so far and what has got Spurs so interested in him?
talkSPORT.com has all the information on the 19-year-old.
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IDOLS
"Growing up my idol was Cristiano Ronaldo," Soonsup-Bell, who owned both Manchester United and Real Madrid shirts as a kid, told the Changsuek YouTube channel in 2021.
"I used to watch clips and skills of him when I was younger and looked at his all-round game. I used to try to repeat his skills and what he did in games."
The youngster also revealed he looked up to Chelsea legends Didier Drogba and Fernando Torres, who he regards as some of the best strikers in football history.
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And during his time in the academy, he was also inspired by former Blues goalscorer Olivier Giroud - his volleys, in particular - and now-Roma star Tammy Abraham's finishing.
POSITION AND STYLE OF PLAY
Given he idolised Ronaldo growing up, the decision to turn him from a midfielder into a striker at Cobham proved to be the correct one.
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One performance that demonstrated the teen's natural scoring ability was when he netted four goals in an 8-1 FA Youth Cup win over Barnsley in November 2020.
Those goals made him the first Chelsea player in 59 years to score four times in the competition.
"Chelsea saw something Swindon didn't see," the starlet's older brother told Goal in 2021. "But that technical side he learned in midfield and that unselfish side helps him as a striker.
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"Chelsea saw that he could score goals but contribute more to mould him quickly into a centre forward.
"He is athletic, as a No.9 should be, and he is quite tall and quick. But, for me, his best attribute is his intelligence both on and off the ball. He has the brain for the sport, with composure on the ball.
"He is right-footed but he spent years working on his left foot when playing football in school, and now he would say he doesn't have a weaker foot. The athletic side is also coming into his game more now."
The teenager has found the net with a number of overhead kicks and backheels in the last few seasons, too.
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CHELSEA CAREER
Just two months after his FA Youth Cup display, Soonsup-Bell signed his first professional contract at age 17.
Fast forward to the end of that year, and former manager Thomas Tuchel gave him his full senior debut in the League Cup, as the Blues beat local rivals Brentford 2-0 victory.
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Soonsup-Bell was aged just eight when captain Cesar Azpilicueta - who featured in the game against the Bees - made his Chelsea debut in 2012, but he impressed in his 45-minute display.
And the teenager sacrificed a lot to get to that point, originally making four-hour round trips to Chelsea training when he first signed before eventually moving in with a host family closer to London.
However, since Tuchel handed him his first minutes for Chelsea's first team, Soonsup-Bell has been pushed down the pecking order at the club and is playing in the club's Premier League 2 squad.
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The forward scored 29 goals in 78 appearances for the various youth squads, with two of those coming the 14 appearances he's made this season.
INTERNATIONAL CAREER
Despite not currently being part of Chelsea's first team plans, the teen has been making the cut with England's youth teams.
The youngster - who is also eligible to play for Thailand thanks to his grandfather - started for the Under-19s in a friendly against Italy and scored last season, as well as playing from the Under-17s and 18s.
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He's also the third highest scorer for England's Under-16s with six goals in nine appearances, just behind Manchester United's Jadon Sancho's six in eight, and Aston Villa's Louie Barry's seven in 10.
It's easy to see why club scouts across Europe - including Spurs - regard him as one of the best strikers in his age group, then. Only time will tell if Chelsea missed out on a promising, homegrown talent.