The 22-year-old notched in his tenth French top-flight goal in 2025 since joining Monaco in January in Friday night's 3-0 win over Reims.
Biereth, who was part of the Gunners' Hale End academy, was sold to Austrian side Sturm Graz for just £4million last summer.
Monaco then came calling during the winter transfer window after the Denmark youth international banged in 14 goals from 25 games.
And he has made the £10.7m Monaco forked out on him look like a bargain after yet again hitting a treble for Adi Hutter's side.
The youngster, who never featured for Arsenal's first team, previously scored hat-tricks against Auxerre and Nantes, while also getting on the score sheet against Rennes.
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Reims have proved to be his latest victim, with Biereth's 17-minute treble lifting Monaco up into fourth spot.
In doing so, he has become the first player since 1955 to score as many hat-tricks in their opening seven Ligue 1 matches in the last 70 years.
But more impressively, Biereth now boasts more league goals than Mohamed Salah, Harry Kane, Erling Haaland and Kylian Mbappe in 2025.
In fact, no player has found the back of the net on more occasions than Biereth in Europe's top five leagues this year.
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With ten strikes to his name, he has scored once more than Paris Saint-Germain's Ousmane Dembele and Atalanta's Mateo Retegui.
Liverpool's Salah and Crystal Palace striker Jean-Philippe Mateta both then follow having been on target eight times each.
In all competitions in 2025, Biereth is level with Salah on ten goals.
Meanwhile he has scored more than Haaland, Kane and Cristiano Ronaldo, who have all banged in nine.
His stunning form may have Arsenal ruing their decision to part ways with Biereth with the club without a recognised centre-forward currently.
With Kai Havertz and Gabriel Jesus both out with season-ending injuries, Mikel Arteta has turned towards central midfielder Mikel Merino to lead the Gunners' line.
Arsenal's lack of firepower up top has all-but ended their Premier League title challenge, as they now trail leaders Liverpool by 13 points.
Biereth will be hoping to continue his hot streak in Monaco's Ligue 1 clash with Toulouse next Friday night.
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