The teenager made his Scotland senior debut yesterday evening.
He played as Scotland picked up a 1-0 win against Denmark, courtesy of Bournemouth winger Matt Ritchie taking advantage of Daniel Agger’s shocking defending.
The teen, born on the Isle of Man, has previously represented Scotland at under-18 and under-19 level. Scotland boss Gordon Strachan threw him straight at the deep end with a start against the Danes.
Tierney has now been discussing his first cap for his country, telling the BBC:
“I don't think anyone could have predicted this is the way the season would have gone for me so far, so I just hope it can continue.
"I'm delighted obviously to make my debut, but it was an important win for us and a good clean sheet again."
"I was excited and surprised [to be selected] but I've been surprised every time I've been on the Celtic teamsheet.
"It wasn't so much bad nerves. Everybody's the same obviously - your first cap, a bit of nerves before. But it's nothing negative. You need to make it positive.”
It was a memorable night for the Celtic teenager – who excelled in his first appearance.
It is easy to forget that the defender is just 18-years-old, especially on the evidence of performances like this.
The teenager has been a revelation at Celtic this season.
His performances in the Bhoys first-team have been fantastic this season and has seen him replace Honduran veteran Emilio Izaguirre as the number one left-back choice for Celtic throughout the campaign.
Hopefully this just the start of a glorious international and club career for Celtic’s newest youth product.