Rewind a few months and Kieran Tierney was nowhere near the first-team picture at Arsenal. So much so that when an early return to Celtic, on loan in January, did not happen, it was seen as an unnecessary move on the part of Mikel Arteta. Since then, the Scottish left-back's role has grown and surprisingly, it is not in defence but as a winger.
Tierney came on as a substitute against Real Madrid in Arsenal's historic 3-0 win against the Spanish club in the UEFA Champions League. Declan Rice scored two unbelievable free-kicks and Mikel Merino added a third in what was Arteta's greatest night as a manager so far.
Of course, we have seen 3-0 first leg leads be overturned in the Champions League in the recent past. FC Barcelona were in the same position as Arsenal in 2019 but ended up losing 4-0 against Liverpool in the second leg.
Arsenal will be hoping to avoid a repeat of that. And do not be surprised if you see Tierney feature once again when the two teams meet at the Santiago Bernabeu.
Celtic-bound Kieran Tierney featured for Arsenal against Real Madrid in the Champions League
More than anything else, Arsenal fans seemed baffled by the turn of events that had brought their team and Tierney to this position. Most seemed happy for the Scottish international, who has already agreed a pre-contract agreement with Celtic to join them as a free agent in the summer.
One wrote: "Kieran Tierney on for Arsenal in a Champions League game against Real Madrid. What a few turbulent years he's had."
Another added: "Tierney against real Madrid this is truly beautiful."
A third said: "Tierney making an appearance was the icing on top. Best day of my life."
One summed up the Celtic-bound left-back perfectly: "Kieran Tierney is what we call a professional. He came in and balled in his first season. Got derailed by injuries. Loaned out to La Liga. Came back injured. Recovered and trained every single day without complaining. Got back into the squad and is getting minutes."
A lot of Celtic fans were unhappy when Tierney's return failed to materialise in the winter itself. Back then, the fear was that he was just going to waste another half-a-season of his career sitting on the bench.
In hindsight, it has proven to be great for all parties involved. Last night was an invaluable experience for the Scot, albeit a short one. Overall, he has featured in three straight Champions League games for Arsenal and four of the last five in the Premier League.