Thelwell, 20, was selected with team-mates Luke Young and Ledley King for the England Under-21 squad for Tuesday night's Nationwide friendly against Spain at Birmingham City.
It was just reward for the young defender who has grasped his chance after being thrown in at the deep end for his Premiership debut against Liverpool in November.
Thelwell, set to sign a contract extension at the Lane, said: "I didn't think about the England set up, I just wanted to try and get back into the Tottenham team.
"It was a real boost to be called up. I delighted with that and will be proud to play for my country if I get the opportunity.
"The new manager is in place, it's a new set up, I'm sure he'll be watching the game and there is an opportunity to impress him. If I play I'll give it my best shot."
The defender was once on standby for England Under-18s but this time has joined up with coach Howard Wilkinson and his cream of the young crop.
"It was a shock at first," he added. "I was at training on Friday and I didn't know but Stewart Houston came up to me and said 'congratulations, you are in the squad'. It was a real shock but I'm very happy."
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Alton Thelwell has admitted his shock at his first international call.