The Leyton Orient midfielder grew up playing with the England internationals in Chelsea’s academy from the age of seven.
The best friends, who were remarkably born within four days of each other in January 1999, were separated when Rice was released from the Blues as a 14-year-old in 2014.
Bexley-born Kemp, a former England Under-20 international, told talkSPORT he was ‘shocked’ by Rice’s sudden exit, which ‘no one saw coming’.
He said: “It was really upsetting, but also the massive thing was how much of a shock it was.
“None of us saw it coming. Even at that age, he was such a good player. It was such a massive shock to see him go because I never thought for one minute he’d be released.
“I always thought he was going to get another contract because it didn’t even cross my mind that he would get released. It was tough.
“To this day, I couldn’t really think of a reason why they would release him. I suppose they had their individual reasons, which we’ll probably never, ever know.
“All I could do as a mate was be there and support him.
“I knew he’d be on to bigger and better things and that he’d have the resilience to bounce back.”
Kemp was right as Rice joined West Ham soon after his Chelsea departure and has gone on to play 139 times for the Hammers’ first-team.
Meanwhile, Mount has established himself as one of the first names on the team sheets for Chelsea and England.
Kemp, who won youth tournaments playing in a midfield three with Rice and Mount at Chelsea, is not surprised by the success of his close friends.
The former West Ham and Chelsea trainee said: “From that young age you can always tell. I played with so many talented players.
“We were all good technically and there are so many good players, so you had to have something different and those two, their mindset set them a part from the rest.
“They work hard every single day, they’re so driven to get better every single day. That goes such a long way.
“Their ability to process information, they’re so intelligent on and off the pitch, which allows them to do exactly what they’re doing, which is thriving and doing so well in the Premier League.
“I’m so proud of both of them.”
Rice had been heavily linked with a big-money return to Chelsea during Frank Lampard’s time in charge, which ended when he was replaced by Thomas Tuchel in January.
And Kemp has admitted it would be ‘amazing’ to see Rice and Mount playing together at club level again.
“Personally, it would be great for them to play together. I know they love playing together for England,” he continued.
“So if that did ever happen, it would be amazing. But they’re both doing so well individually for their clubs that, for me, whatever did happen, they’d love to play with each other again – wherever it is.
“I’m sure they’re happy where they are at the moment.”
Kemp insists Rice and Mount have the characteristics to become permanent captains of their clubs one day – and possibly even lead the England national team.
At times, Rice and Mount have been on the receiving end of online abuse when playing for the Three Lions, especially the latter, but Kemp has backed them both to play pivotal roles at Euro 2020 and prove the doubters wrong.
He explained: “I see them playing a massive role. For both of them, they’re both very versatile in the positions they play.
“I know Dec hasn’t played there recently, but he can play as a centre-back or as a holding midfielder. Mase is exactly the same, he’s so intelligent as a footballer. He can play in midfield, as a wide man, in and out of possession he’s outstanding.
“There are always going to be different opinions on social media. They’re both so mentally strong and they believe in themselves, so I don’t think they’d let any of that get to them.”
Kemp’s journey has been different to the one Rice and Mount have taken.
He left Chelsea during his first-year scholarship to join West Ham on a professional deal in 2016.
Loan spells followed at Stevenage and Blackpool, and without a senior West Ham appearance to his name, Kemp made a permanent switch to Leyton Orient in January.
While he plies his trade in League Two, Kemp has plans to emulate Rice and Mount by playing in the Premier League.
He said: “I’ve really enjoyed my start at Leyton Orient.
“For me, my dream and ambition has been to be a Premier League player. I still believe I can achieve that. It’s just about showing everyone what I can do on a consistent basis.
“I’ll be working my hardest every single day to get up to the levels I want to get to.
“Dec and Mase are always looking out to see what I’m doing. They’re always behind me, 100 per cent. They believe in me. They’re always the first ones to message me if I score.
“They’re so supportive. I’d be silly not to ask for advice and tap in to their experiences as well.”