The Young Lions' manager included Bellingham in his most recent squad.
And it only took a training session for the former Birmingham man to show his quality.
"When we got on the pitch, you couldn't tell he wasn't an Under 21 player," said manager Boothroyd to reporters of the teeanger.
"That's why they are where they are. Humility is a trait of successful people. He's got it in abundance. My first impression is that he is a very impressive young man on and off the pitch."