Heidi Klum left her son Henry gobsmacked with his special 21st birthday gift.

The 53-year-old model and her 37-year-old husband, Tokio Hotel guitarist Tom Kaulitz, pulled out all out, splashing out on a red Ferrari F430 worth more than six figures, to celebrate his special day on Saturday (12.09.26).

In a video shared on Instagram, Henry appeared stunned as he walked out of the family home with his stepdad following behind, and saw his new flashy sports car waiting for him in the driveway.

As he caught a glimpse of the Ferrari, Henry exclaimed: "Oh my God! Jesus Christ. I don't even know what to say."

Recording the special moment, Heidi said: "I can't believe it is that time. You've been waiting for so many years."

As Henry and Tom marvelled at the vehicle, the latter explained he bought it at an auto show "last year" and hid the Ferrari in the garage "the whole time".

Henry said: "This thing is beautiful. Holy s***! Oh my f****** God, this … is insane. Holy s***, this thing is crazy."

Project Runway host Heidi noted that Tom "kept his promise" after losing a video game bet to a 14-year-old Henry, which meant he had to buy his stepson a Ferrari when he turned 21.

She said: "Literally, it's what? Seven years ago when you guys said that?"

Also on Saturday, Heidi shared the clip where Henry and Tom made their Mario Kart bet.

The then-14-year-old said: "It's happening on Christmas, and if I lose Mario Kart, then I can't play video games for three months, and I have to give him a painting of me driving.

"But if I win, then Tom has to give me a Ferrari when I'm 21."

As well as Henry, Heidi has a 19-year-old son named Johan and a 16-year-old daughter called Lou with her 63-year-old ex-husband, singer Seal.

The beauty also has a 22-year-old daughter named Leni with her 76-year-old former spouse, businessman Flavio Briatore.