The Keeping Up with the Kardashians​ star, who turned 18 last month, is featured in the video for Tyga's​ new track, Stimulated.

The song makes various references to Kylie and Tyga's relationship, particularly their seven-year age gap.

"They say she is young, I shoulda​ waited," Tyga, 25, raps in the song. "She a big girl, dog, when she stimulated."

The song continues: "She a big girl, dog. I'm puttin' in. Yeah, I'm penetrating."

Despite the song's lyrics, Kylie's presence in the video is relatively PG.

The youngest Kardashian sister, who recently moved out of her family home into a $US2.7 million ($3.64 million) Los Angeles property she purchased herself, is shown entering a luxurious beachside mansion.

Other shots scattered throughout the video show Tyga piggybacking Kylie across the grass, before the couple stop to kiss and embrace.

In addition to the release of the Stimulated video, Kylie and Tyga made their first joint public appearance this week.

The pair attended the MTV Video Music Awards, sitting next to Kylie's mother, Kris.

Her sisters Kim and Kourtney​ Kardashian also attended the ceremony, during which Kim's husband, rapper Kanye​ West, announced his intention to run for the US presidency in 2020.

Kylie Jenner and Tyga have been in a relationship since early 2015. At the time, Kylie was still 17 years old, making her below the age of consent under Californian law.

When the pair first indicated that they were seeing each other, their age gap was a source of controversy, although the teenager's family jumped to her defence.

Kylie's older sister Khloe​ Kardashian​ told Complex in July that the relationship was justified because Kylie was "not a normal 17-year-old".

"You're not gonna say, 'Hey, so what are you doing this weekend?' and have her say, 'Having a slumber party at my girlfriend's' or 'Going to prom'. That's not what Kylie does," she said.

"Kylie is taking business meetings and bought her first house, or she's going on a private plane with Karl Lagerfeld to take a meeting. That's not even what people do in their 30s. It's a rare circumstance, so let's treat this as a special case."

However, according to RadarOnline, the Kardashian family – who are committed Christians – are upset with how their daughter is portrayed in the song, which is the first off Tyga's new mixtape​, Fuk What They Talkin Bout.

A source told the online tabloid the song's lyrics are "so disgusting that the Kardashian​ family cannot even believe Tyga went there".

"Tyga knows not to discuss Kylie with anyone and then he goes and writes a song about having sex with her," the source said. "It is just absolutely repulsive!"