The teenager made a huge impact in Serie A after scoring a double as Roma beat Genoa 2-0 a month later.
He became part of the first team and made 20 appearances in all competitions, while helping Roma win the Europa Conference League.
Afena-Gan secured a move to newly promoted Cremonese from Roma last summer but has fond memories of his time under Mourinho.
“Mourinho is my second father. He made me who I am today. The 19-year-old told La Gazzetta dello Sport, as quoted by 3Sports.
Meanwhile, Afena-Gan became the captain as Cremonese knocked Napoli out of the Coppa Italia.
Cremonese qualified for the quarter-finals of the Cup competition after beating Napoli on penalties on Tuesday evening.
The visitors took an early lead thanks to Charles Pickel’s brilliant finish in the 18th minute after being set up by David Okereke.
However, quick-fire goals from Juan Jesus and Giovanni Simeone turned the game around as Napoli took a 2-1 lead into the half-time break.
Afena-Gyan replaced Okereke in the 65th minute and grabbed a late equalizer to send the match into extra time.
The 19-year-old striker then scored the winning penalty as Cremonese ran out 5-4 winners in a shootout against the Seti A leaders.
“Amazing team effort tonight. Congratulations to @USCremonese for qualifying to the next stage of the #CoppaItalia . If we believe, we can achieve,” He later wrote on Twitter.