The former Scarlet was approached to play for Scotland last season but was ineligible after playing for Wales Under-20s - with the International Rugby Board ruling in Wales' favour.
Now the 21-year-old is eyeing further international honours with Wales, having seen his brother Aaron make his senior debut during the RBS 6 Nations
"It was obviously a bit of a roller-coaster at the start. It led on with a few hearings and generally it didn't go Scotland's way," said Shingler.
"I made a decision early on when Andy Robinson offered me the chance to play international rugby.
"He told me 'in about two weeks you're going to start at 12' and it was one of those, you can't really turn it down.
"But in hindsight after watching Wales win the Grand Slam and realising how it all went I had a chance to reflect on it a bit more.
"It was a long time ago and I feel like saying I was quite young and maybe naïve and didn't really think it through too much.
"Andy phoned me up he obviously knew I was Scottish and I hadn't really considered it before then and it was one of those things.
"Obviously it's different when all this is out in front of me I can obviously say it was the wrong decision to make but that's the way it goes.
"I was brought up in a Welsh shirt and that's where I hope to be heading."
But for now the promising back is just concentrating on life in the Aviva Premiership with the Exiles.
Shingler has his eye on playing fly-half but will have added competition this season after Irish bolstered their fly-half options.
"I just want to be focusing on playing for London Irish and whether that opportunity to play international rugby comes again is great and if not, so be it.
"I wouldn't mind playing fly-half but I have a battle on my hands to play 10 at Irish with Shane Geraghty and Ian Humphreys. That's what I'm fighting for now."