From competitors, to friends, to downright enemies.

Rex USA

Jef Holm is trashing the new "Bachelor," Arie Luyendyk Jr, who he competed against for Emily Maynard's heart on season 8 of "The Bachelorette" in 2012.

Jef, who had a short engagement with Emily in 2012, became friends with Arie, Emily's runner-up, after the couple split. At the time, the two were spotted at various events and even joked on Twitter that they needed to do a show about their bromance.

But things have drastically changed in the past few years, and Jef is not happy about Arie being the newest "Bachelor."

After the announcement about the race car driver being named the 22nd "Bachelor" on "Good Morning America," the 35-year-old former People Water executive tweeted, "Oh the stories I could tell…"

But he got really nasty responding to a tweet from blogger Reality Steve, who posted a screenshot of an anonymous comment about Jef and Arie, also 35, hooking up with sorority girls. "The word on the street is that he's been doing this for years, and was wing-manning for Jef. Apparently the number of young college girls who have hooked up with him, in one sorority chapter alone, is absolutely obscene," the commenter wrote about Arie. "Him and Jef would make regular appearances at their parties."

Jef replied to the tweet, "I've actually never even been inside a sorority house. As for him...I stopped being friends with him years ago because he's disgusting."

However low Jef's opinion is of Arie, it doesn't really matter, because Emily -- who is pregnant with her fourth child -- still thinks very highly of him.

"I can't think of a better person to be The Bachelor than Arie and I've been hoping this day would come since Season 8 ended!" she exclusively told Us Weekly in a statement. "He's a gentleman through and through and all the girls on his season are lucky to have him."