The Tshwane giants forked out R13,2 million for the talented Sout African forward's services on PSL transfer window deadline day.
However, the 20-year-old winger struggled to establish himself at Al Ahly and he has since returned home.
Goal takes a look at the possible reasons why Mahlambi returned home and whether or it's good for him and his future. We also look at his chances of moving to Europe after signing a long-term deal with Sundowns.
CHANGE OF COACHES & LACK OF GAME TIME
Some expected Mahlambi to hit the ground running in his first stint outside the country due to his unbelievable talent despite being only 19.
However, his first challenge was to adjust to a new environment in Egypt.
Former Al Ahly coach Hossam El Badry, who had backed the club's decision to pursue Mahlambi's services, helped the player adjust to life in North Africa and he gave him the platform to showcase his talent.
But that was before he resigned as Al Ahly coach following a shock defeat to Ugandan side Kampala Capital City Authority (KCCA) in the 2018 Caf Champions League Group A game with Mahlambi playing 58 minutes of that encounter.
This proved to be Mahlambi's last match in the Champions League as Hossam was replaced by French mentor Patrice Carteron, who opted for more experienced attackers.
A lack of game time left Mahlambi frustrated at Al Ahly, and reports of his indiscipline emerged at the beginning of the current season.
The former South Africa under-20 international was financially sanctioned by Al Ahly after missing training without notifying the club.
It was quite clear that Mahlambi was unhappy at the Cairo-based side, and he was prepared to leave in search of regular game time.
BAFANA & RELAUNCHING OF CAREER
The Johannesburg-born player's promising career became stagnant at the Red Devils during his one-year spell with the club, and he wasn't growing as a player.
This also meant that Mahlambi would not be considered by South Africa coach Stuart Baxter, who unsurprisingly left him out of the Bafana Bafana squad for the upcoming 2019 Africa Cup of Nations (Afcon) qualifier against Libya.
With the Afcon finals a few months away, coming back home will be seen as a way of getting back into the Bafana Bafana team.
Mahlambi has been tipped by many to be one of the most successful players in the history of South Africa, and the only way to make it to that level is playing as many international matches as possible with Bafana Bafana.
A move back home made more sense for Mahlambi, and it could go a long in ensuring that he reaches his full potential.
SUNDOWNS STEPPING STONE INTO EUROPE
Sundowns maintained their interest in Mahlambi since last year which showed how serious Pitso Mosimane's side was about the star attacker.
While working with a coach who appreciates your talent may bring the best out of you as a player, Mahlambi's long-term dream will be to go to Europe.
The Brazilians, although they have a reputation of wanting to hold on to players even with European offers on the table, have already helped Bongani Zungu, Keagan Dolly and Percy Tau move abroad by giving them the platform to shine.
Tau recently left Sundowns for English Premier League club Brighton and Hove Albion at the age of 24, and this success story may have motivated Mahlambi to go to Chloorkop.
Many would agree that Mahlambi is destined to ply his trade in Europe, and it could be one of the reasons why the gifted player decided to join Sundowns in order to be exposed to Caf Champions League football.
Sundowns, with their ambition to conquer Africa, are the perfect club for Mahlambi, but he will have to work extra hard to cement his place in the team full of quality and depth.