WE all knew it was going to happen.

The moment Kieran Tierney burst onto the scene four years ago as a 17-year-old, which is when he made his debut, and who played as if he was a seasoned pro, I quickly concluded that one day a club from a bigger league, and importantly with a lot of money, would come in with a record bid.

It didn’t take long for most of us to realise the Celtic had produced a real gem. The best we’ve seen in a long time. That this was a lad who could play anywhere he wanted. Keeping Tierney a secret was never on the cards.

Arsenal bid £10million for him when he was 19. That was knocked back. They were never going to go away forever. Everton had a nibble a year ago. God knows how many other clubs have sent a scout to Celtic Park

KT was always, one day, going to say his goodbye to the club he will always support to go on an adventure.

I wish the day had not come, but it has.

Tierney goes with my good wishes and heartfelt thanks for four incredible seasons. Arsenal have done well to get him for £25million and I’m sure most Celtic supporters, while disappointed, understand why one of their own is now an English Premier League player.

How good is he? I was fortunate to play with Tommy Gemmell and Danny McGrain. I have no hesitation putting young Kieran in that bracket in terms of the great full-backs produced by Celtic.

My guess is that Tierney didn’t want to leave Celtic. There was no banging on Neil Lennon’s door, he didn’t put in a transfer request and never once spoke about playing elsewhere.

However, some opportunities are too good for anyone to turn down.

You get one crack at this. Football is a great job but can be taken away from anyone. My own career was cut short by injury so I know what I’m talking about.

This is a man’s life we are talking about. He gets to choose what he does with it. Nobody else.

The past three years have been some of the best times to be aCeltic fan and player - he’s both - and few if any have contributed more to the triple Treble than Kieran Tierney.

Arsenal haven’t won so much in recent times; however, we are talking about a huge club in a fantastic league, and it’s a team which I believe is getting better.

I have no fear about Tierney being good enough. He is going to be a sensation.

One thing that has been lost is that this is a huge feather in the cap for Celtic’s academy. They found him, trained him and now he’s become the most expensive Scottish footballer of all time.

That’s not a bad return for your money – which was nothing.

Against Cluj, Callum McGregor was outstanding, James Forrest scored another brilliant goal, both came through the ranks.

And we will see Liam Henderson in Serie A next season.

Not only that, but there are lots of former Celtic academy players earning a living out the game in the Premiership and elsewhere.

Chris McCart and the staff at Lennoxtown deserve a lot of credit.

The most praise goes to the player himself. For a lad from Motherwell to become a hero for his team and then to make his club a fortunate at only 22, tells you how much he has given to his profession,

That won’t change at Arsenal. The bright lights of London won’t get in the way of his progress. Watch him go.