After watching the Reds in action on Thursday night, Allen honoured Brendan Rodgers' pledge to tie up a big-money move from Swansea within 24 hours. The 22-year-old midfielder has signed what is being termed as a long-term contract, to become Rodgers' second signing as Reds boss.
It completes a remarkable rise from League One, where he made his Swansea debut as a teenager, and asked if he would have believed five years ago that this day would come, Allen said: "No, probably not. It was hard to believe at first and very flattering to be linked to a top club like this."
He added: "It shows you're doing something right, I guess. I've always been ambitious and wanting to get to the top but getting there is a completely different thing. It's definitely hard to believe. It's been a quick rise for me."
Whilst there have been plenty of Liverpool supporters expressing doubts over Rodgers' appointment following the exit of club favourite Kenny Dalglish, Allen has none.
The Northern Irishman has guided him through the latter stages a career that took him into the Premier League and, most recently, Stuart Pearce's Olympic side.
And with this season's opener at West Brom just seven days away, Allen admits he cannot wait to get started.
"To join back up with him was definitely a big pull for me," said Allen. "Brendan is so passionate about his football. He works day in, day out to improve the team and everyone individually.
"Everyone wants to work alongside someone who has that way about them. One of his best things is his man management. He commands the respect of everyone.
"I have a lot of faith that Brendan can bring success. I wanted to be part of this project and I've really got a good feeling this football club is going to go from strength to strength in the next couple of seasons."