But the ex-Aston Villa captain couldn't help but crack a Second City derby-themed joke when talking about the teenager's impact at the 2022 World Cup.
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Football history suggests the England stars shouldn't be friends, given they both came through the ranks of rival clubs Aston Villa and Birmingham City.
But despite this, ex-Blues star Bellingham has recently told talkSPORT the former Villa skipper made him feel more than welcome in the England camp, giving him a massive hug when they first saw each other.
Despite being just 19-years old, Bellingham has been one of the most important players for England in Qatar - and Grealish revealed he's full of admiration for his old club's former rival.
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"Yeah, no he's been brilliant," he said. "I didn't honestly expect anything else, the way he's started the season playing for Dortmund. Even in the Champions League he's been on fire so I didn't expect anything else.
"It's crazy to think he's only 19 years old and the way he plays you know he's so mature.
"You know I think we've all seen players in the past that have been so good but you can tell that they're young by the way they've played.
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"But he plays like he's a 25, 30-year-old player that's being playing at the top for years. He's got everything honestly, he can defend, he can tackle, he can run, he can dribble, he can score, he can assist.
"So you know, fair play to him."
Of course, both players have long since moved on from their first clubs, with Grealish signing for Manchester City in 2021 and Bellingham playing for Borussia Dortmund since 2020.
But Grealish has shown that the phrase once a Villan, always a Villan, will always ring true for him, as he joked there is one Blues-related flaw in his England teammate.
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"There's another thing that's so good about him as well, he's a really lovely kid you know at heart," Grealish said. "He's a fellow Brummy as well.
"Just a shame he doesn't support Aston Villa! That's the only problem with him."
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