Alexander-Arnold was named in the preliminary 23-man squad yesterday.
"It was an unbelievable moment to find out I was going to go to the World Cup, especially at a young age. It's probably capped off a really good season for me," he told the club's website.
"I found out (on Wednesday) morning, just before we came out to Marbella. The manager came and spoke to me just as we were getting on the plane.
"He asked me if I knew anything about the squad or anything yet. I said, 'No' and he said, 'Have you got anything planned around the time of the World Cup?' I was like, 'No, no holidays or anything…'"
"He said to me, 'OK, good… You're in the squad!' It was a really proud moment. On England's behalf, it was nice of them to let the manager tell me."