Part of the side that won the Under-17 World Cup in 2017, the Chelsea winger has been subject of sustained interest from Bayern Munich, having made his first-team breakthrough at Stamford Bridge this season.
The 18-year-old has yet to start a Premier League match for Chelsea, but Gareth Southgate has promoted him to the senior squad after Manchester United's Luke Shaw became the fourth player to withdraw through injury.
It was a whirlwind day for the teenager, who had been in Bristol preparing for his first taste of international Under-21 football with Aidy Boothroyd's side when the call came.
Hudson-Odoi had barely finished his lunch with the Young Lions before heading up to St George's Park to join the senior team for the Euro 2020 double-header against the Czech Republic and Montenegro.
"It's been a crazy day but getting my first (senior) international call-up is an amazing feeling," the 18-year-old said.
"Today has been a very long day for me because I had to travel to Bristol first for the U21s and then getting told that I have to come over here to St George's Park.
"It's been a crazy experience but I'm delighted to get the call and it's a nice feeling to be here as well.
"I thought the manager was joking. I was shocked and then when I heard that I actually had to go over, I couldn't believe it. I was delighted.
"It's a dream come true. Now I've got to work hard, enjoy every moment and keep working to just hopefully make an impact when I get the opportunity.
"Everybody here is very humble and they're very nice. They make sure you're comfortable, no one has an ego here so hopefully I get to know more of the boys here."
Hudson-Odoi had already been in the news on Monday after Chelsea confirmed they had lodged a formal complaint with UEFA over racist abuse aimed at the player during the closing stages of the 5-0 Europa League win away to Dynamo Kiev last week.
The 18-year-old scored in the Ukrainian capital and will become the youngest Chelsea player in history to play for England if he makes his debut this month.
Hudson-Odoi was the second new addition to the squad after in-form Southampton midfielder James Ward-Prowse linked up with the Three Lions earlier in the day.
There was some surprise about his omission from the 25-man squad named last week and Southgate had no hesitation in turning to his former Under-21 captain after Fabian Delph, John Stones and Ruben Loftus-Cheek pulled out of the squad.
Delph was replaced less than an hour into Manchester City's FA Cup quarter-final win at Swansea, which team-mate Stones missed with a groin injury.
Loftus-Cheek came on as a second-half substitute as Chelsea lost to Everton on Sunday and has now been replaced by former Young Lions team-mate Ward-Prowse.
The 24-year-old has flourished under Saints boss Ralph Hasenhuttl, who has helped add aggression and goals to the midfielder's game.
Ward-Prowse has scored six goals since the turn of the year, including stunning free-kicks in Southampton's last two matches.