The rapper is thought to have given Bieber the car on March 1 for his birthday.
According to People, Bieber was not expecting to receive the gift from Diddy.
The singer previously said: "He said when I turn 16 he will give me his Lamborghini.
"But we all know Diddy's not going to give me his Lamborghini, he's all talk."
The teenager was apparently given a Range Rover from Usher for his 16th birthday also.