"Juan Pablo doesn't care about you at all. He's a total zero, and if you've really fallen for him, this bum will only break your heart!" McDill, 27, warned Ferrell in Star magazine's March 24 issue.
"I watched the show against my better judgement, only because Nikki was on it, of course. It was surreal to watch someone who I've been so close to. And from what I've seen of Juan Pablo, he has nothing going on, other than being handsome. He's dull, has no personality, is a terrible listener, is totally self-centered, and doesn't seem to be too bright. I know Nikki as well as anyone, and it would be a huge mistake for her to get wrapped up in this loser."
McDill said he began dating Ferrell, 27, in July 2012 after they met in their home state of Missouri.
"Our first date was at a Country & Western bar. She loves that scene -- but she hates Latin music. That could also be a problem with Juan Pablo," McDill said of the Venezuela native.
Ferrell and McDill broke up last July, shortly before Ferrell left to filmThe Bachelor's eighteenth season and fell in love with Galavis, a Miami, FL resident. She eventually received his final rose without a proposal or even an, "I love you."
"She was absolutely ready to settle down, but I wasn't quite there. And I think it'll be deja vu for her with Juan Pablo," McDill told Star.
"He talked about doing right by his daughter -- while he's whoring around on TV. He wasn't man enough to marry the mother of his child -- and he wasn't even man enough to tell Nikki he loves her. How pathetic is Juan Pablo to refuse to say you love a woman on a show likeThe Bachelor? But frankly, I was floored that Nikki just sat idly by after that. That's not the Nikki I've ever known."
McDill expressed the same notion to Us Weekly recently.
"She normally wouldn't take that s--t from a guy," he told the magazine. "The Nikki I know would have slapped him and walked out."
Ferrell's ex-boyfriend just doesn't see things working out between the couple in the future.
McDill told Star, "Frankly, the prospect of Juan Pablo settling down seems far from reality. And if he leads Nikki on, she'll have to debate moving to his home in Florida, or to California if he wants to have a showbiz career, like everyone says. He'd never adjust his life for her -- and ultimately, he'll screw her over."
"Girls who date Juan do what he wants," a source told Us.
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McDill added that Ferrell is "caring, sweet and not stuck up at all" despite her questionable edit and how her fellow bachelorettes perceived her during the season. He noted that he still has feelings for her deep down and wants the best for her.
"We've both moved on, but we still talk, and a part of me will always love her. If Juan Pablo ever did anything to really hurt Nikki, I would waffle-stomp his ass!" Ferrell's 6'3" and 215-pound ex-boyfriend explained to Star.
But even show insiders apparently believe Galavis will end up hurting Ferrell.
"In my opinion, the chances that Juan Pablo will carry this through to marriage because he genuinely has feelings for Nikki are the same as either of them being hit by lightning, about a million to one!" an insider said.