England fly-half Marcus Smith will join up with the British and Irish Lions squad in South Africa as cover for Scotland's Finn Russell.
Russell, 28, is ruled out until the start of the three-Test series on 24 July with an Achilles problem.
Smith, 22, was told the news when he came off in the second half of England's 70-14 win over Canada.
"I thought I was being told off, had made a mistake or done something wrong," said Harlequins star Smith.
"But they shared the news I was flying out tomorrow which was special news to hear and I had to get my breath back because I was massively overwhelmed. I had no clue."
Smith has caught the eye with a series of dazzling displays in Harlequins' run to the Premiership title and made his England debut last week against the United States.
"I don't even know what to pack - my mum is going to help me - but I'm over the moon and will have to have a few beers to settle the nerves a little bit," he added.
"It was always my dream to represent the Lions. I didn't expect it to come this soon.
"It's been a whirlwind few weeks, and a whirlwind 45 minutes to an hour.
"I will try and take it all in, but I don't think I will until I get out there."
The only downside for Smith is he is now unable to attend the Euro 2020 final at Wembley on Sunday after getting tickets to England's match with Italy.
"We were meant to go but I think I will be on the plane," Smith said in a state of shock. "England are going to win, 2-0. It's coming home!"
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His free-running style, similar to Russell, brings an attacking threat at 10. However, he has only just broken through at international level.
He won his first cap when a new-look England team beat the United States 43-29 - and made a second appearance against Canada on Saturday, scoring 18 points in their victory at Twickenham.
Lions head coach Warren Gatland said: "We're obviously disappointed for Finn, who I think has been outstanding since he came into camp in Jersey, but we are optimistic he'll still play an important role in the Tour.
"We have two experienced fly-halves in Owen Farrell and Dan Biggar, so it's a great opportunity for the continued development of Marcus.
"Finn and Marcus are similar in that they like to play with a bit of freedom, so, for me, it's as close to a like-for-like cover as we can get."
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