The Saints midfielder was today drafted in by Three Lions Manager Roy Hodgson for the FIFA 2014 World Cup qualifier against Ukraine on Tuesday evening.
Lallana had previously been capped at Under-18, Under-19 and Under-21 levels but this represents his first-ever involvement at senior level.
And the 24-year-old spoke to saintsfc.co.uk
minutes after his place in the squad had been confirmed to give his reaction to the news.
"I'm totally shocked to be honest, and I didn't think the gaffer was being serious when he called to tell me this morning," he admitted.
"I was at home about to head into the training ground when he called – I think I must have asked if he was having me on a dozen times!
"It's such a proud accomplishment to be called up to play for your country at any level, but to be called into the senior side is probably the proudest moment of my career so far.
"To play for the Under-21s was a great achievement but this tops it because it is every player's dream to represent your country at the top level."
Lallana joined up with England too late to be involved in today's training session following the squad's return to the country from Friday's 5-0 win in Moldova.
Nevertheless, Saints' newly-appointed team captain is eagerly anticipating his first taste of senior-level international football at Wembley tomorrow evening.
"I'm looking forward to the experience," he affirmed.
"I've been called up quite late so I'm realistic in accepting I might not be that heavily involved, but the fact that I will be around such experienced international players is something I am really excited about.
"Even if I don't get the chance to feature, it's nice to know that you are in the thoughts of the national manager.
"I have great memories of my last appearance at Wembley in the Johnstone's Paint Trophy final (where he scored in a 4-1 win over Carlisle in March 2010) so I hope tomorrow will give me even more.
"The lads did really well on Friday to get such a positive result against Moldova and I just hope that we can get another good one tomorrow."
Lallana will link up with his former St Mary's teammate Alex Chamberlain in the squad, while it was the withdrawal of another former Saint – Theo Walcott – that opened the door for his call-up.
And he says that his selection is testament to the progress the Club has made over the past few years and the impression it has made during its first games back in the Barclays Premier League.
"I think it reflects really well on the Club, and I think everyone can be proud of it," said Adam.
"It shows just how far Southampton has come to have an English player represented at national level.
"We have a lot of talented young English players here and I'm sure that I won't be the last person to represent our country as some of the young lads can go all the way."