On August 31 2016, Serge Gnabry departed north London after five years at Arsenal.
He returned to Germany having signed for Werder Bremen in a deal worth a reported £5m.
On October 1 2019, Gnabry was back on north London soil for the first time in almost three years and left his mark against the Gunners' bitter rivals Tottenham Hotspur.
In the first Champions League group stage game at the Lilywhites' new stadium, Gnabry scored four times as Bayern Munich ran out 7-2 winners.
As expected, Arsenal fans have been heaping praise on the 24-year-old ever since the final whistle blew in north London.
With that said, there's plenty of regret when it comes to Gnabry as he was on the books at the Emirates Stadium and was allowed to leave for a relatively small fee.
Now valued at around £54million, according to Transfermarkt, not securing the winger to a new contract must haunt the Gunners to this very day.
In honour of Spurs' 7-2 loss, football.london has picked out seven times Gnabry has made the Arsenal regret the decision to sell him in the summer of 2016.
Take a look...
1. Bayern Munich transfer
It's well documented that Gnabry went on loan to West Brom and wasn't deemed good enough by Tony Pulis at the time.
Arsene Wenger also attempted to extend Gnabry's contract, but he opted to join Werder Bremen having felt first-team opportunities at the Emirates would have been limited.
"We didn’t want to get rid of Gnabry, we wanted to keep him. But he was in the last year of his contract," Wenger told ESPN. "We were close to extending his contract but finally he changed his mind and went to Werder Bremen.
"But I think we taught him a lot and I think if you ask him he would agree with that."
The Gunners really should have done more as following a good debut season with Bremen, Gnabry was snapped up by the biggest club in Germany.
2. Germany national team debut
The fact that Gnabry earned a call-up to the senior Germany squad just a few months after leaving Arsenal was another sign that the Gunners had made a mistake by letting him go.
Oh and on his debut he scored a hat-trick - albeit against minnows San Marino - but his eye for goal was impressive that day.
3. Liverpool performances
Gnabry had impressed in Germany for Werder Bremen as well as for Hoffenheim during a loan spell in the 2017/2018 season, but last season was where he was finally given a chance at Bayern Munich.
And there was a lot of intrigue surrounding the Champions League round of 16 clash against Liverpool.
Bayern were favourites to progress, but without Arjen Robben and with Franck Ribery carrying an injury, faith was placed in Gnabry in both legs.
Despite the Reds progressing, Gnabry showed enough in both games to suggest Arsenal made a mistake by letting him go.
Click here for fan reaction after the first-leg.
And here for what Arsenal fans said about Gnabry after the second leg.
4. What he did to Virgil van Dijk
Arsenal fans were once again scratching their heads over how the club allowed Serge Gnabry to slip through their fingers after the Germany winger showed his class in a tangle with Liverpool's Virgil van Dijk.
But this was on international duty back in March.
Cutting inside from the left, he gave the defender the slip to and curled a shot into the far corner to put away a stunning moment of individual skill.
This moment prompted some Arsenal fans to suggest Gnabry had made van Dijk look like Shkodran Mustafi.
5. Brilliant Germany record
10 caps for the national team, nine goals scored.
In fact, it does feel like every time Gnabry's pulls on a Germany shirt he does something special to remind Arsenal fans of what could have been.
Expect him to be one of the stars at next summer's European Championships.
6. Arsenal's lack of goals in wide areas
In every full season since Gnabry has left Arsenal he's reached double figures for goals in the Bundesliga.
All from operating out wide.
Something which the Gunners have struggled with of late, especially last season when Gnabry (13) outscored Henrikh Mkhitaryan and Alex Iwobi (12) across all competitions last season.
There has been efforts to correct this with the £72m signing of Nicolas Pepe this summer, but he's yet to find his best form.
7. Four-goal haul vs Spurs
The Spurs game prompted mixed feelings among Arsenal fans.
On one hand they are delighted to see Gnabry doing so well and scoring four times against Tottenham in their brand new stadium is a massive plus.
However, some are wishing he was doing so in an Arsenal shirt instead of Bayern Munich.
