"It's an incredible feeling but I'm speechless," said Halfpenny who was one of six Blues players and 13 Welsh internationals named in Ian McGeechan's touring party.
"I knew there had been talk in the build-up that I may have a chance of being included. But it was only when I woke up at 5am (on Tuesday morning) that I thought, 'this is actually happening'. I couldn't get back to sleep!"
A nervous wait came to an end just after 1.30pm yesterday when tour manager Gerald Davies read out the 37-man squad and Halfpenny admits that the announcement brought emotional scenes for his nearest and dearest.
"I found out watching the television in my house in Swansea with my girlfriend and my best friend.
"We were all really nervous and then when the announcement came through, I jumped up and nearly hit my head on the light above me.
"Everyone was in tears. I rang my parents straightaway and they were in tears too.
"I've had more than 50 text messages which I haven't even read yet and the telephone hasn't stopped. My battery is running out!"
Halfpenny is one of six Cardiff Blues players selected for the tour alongside team-mates Tom Shanklin, Jamie Roberts, Andy Powell, Gethin Jenkins and Martyn Williams.
The former Wales youth star only made his international debut in November of 2008 having been a member of the Blues Academy and Principality Premiership outfit Cardiff RFC just last year.
After aiming for nothing more than a few appearances in senior Blues colours this season, his rise to the summit of the British and Irish game has been a meteoric one.
"A year ago, I was in the Blues academy and I was just hoping to get a game for the Blues this season.
"But then I got the call for Wales and now this has come along. I would never have expected any of this at the start of the season. It's a massive achievement for myself and my family."
Just like skipper Paul O'Connell and head coach McGeechan, Halfpenny's attentions now turn to ensuring the 2009 Lions end their 10-match tour with a series victory to their name.
Even for a player as a young and new to the professional game as Halfpenny, taking part in a Lions tour is not enough. Earning a Test place and beating the Springboks is now the main objective.
"On tour the one thing you'll want is to get that Test jersey on," added Halfpenny.
"On my first cap for Wales in November I lost to South Africa, hopefully I'll get a chance for revenge.
"We're going there to win a Test series and I can't wait to get started."