Calvin Harris is reportedly worried about new girlfriend Taylor Swift's infamous ex, Harry Styles.

According to OK! Magazine, the Scottish DJ, who is "super-protective" of the "Blank Space" singer, has ordered the One Direction lothario to back off from him, as well as his lover.

Although a source insisted that Harris is "not usually the jealous type," he had no choice but to tell Styles to "stay the f**k away" because he knew "how charming Harry can be and what an impact he had on Taylor."

Moreover, since the "Summer" producer supposedly does not want to get involved in a love triangle with the ex-couple, he has made it clear to the "Steal My Girl" crooner that "he needs to stop sniffing around Taylor."

The source added that Swift "came clean" about the fact she and Styles were still hooking up "until recently," following their breakup back in 2013 -- which Harris "appreciated her honesty."

Meanwhile, the "Shake It Off" singer's new romance with the EDM star might cause best friend Selena Gomez to obsess over her ex-boyfriend Justin Bieber all over again, according to HollywoodLife.com.

The publication previously reported that Gomez's relationship with Zedd could not last, because she still had feelings left for Bieber.

An insider now claims that "The Heart Wants What It Wants" crooner was able to forget about the "Boyfriend" hitmaker for a while -- thanks to Swift reminding her to stay busy and focused on her career.

However, now that she is reportedly busy dating Harris, the "I Knew You Were Trouble" singer may have less time for her pal, who will then likely turn to her on-again, off-again lover, being "more vulnerable to falling into some old habits."