Neil Patrick Harris, Hilary Duff talk Barney's return on How I Met Your Father : 'I broke 100 times'

Almost a decade after How I Met Your Mother ended, Barney Stinson's (Neil Patrick Harris) still got it.

When he returns in How I Met Your Father's season 2 midseason finale (streaming Tuesday on Hulu), the suited-up lothario runs into Sophie (Hilary Duff) — or rather, she literally runs her car into his — at a pivotal moment in her life (check out EW's exclusive sneak peek of their meeting in the video above). And as flustered as Sophie seems when she meets Barney, it turns out that Duff was even more nervous in real life to film these scenes with HIMYM's most legen — wait for it ... — dary  character.

Patrick Wymore/Hulu Neil Patrick Harris and Hilary Duff on 'How I Met Your Father'

"I broke 100 times," Duff tells EW with a laugh. "He had so much to do that day, he had pages and pages of dialogue, and everything that could go wrong went wrong. Some crew guy got hurt and there was an ambulance, it was pouring down rain, of course on the only night that we had him, and we're outside, and we'd already shot stuff leading up to this night where it wasn't raining. Thankfully it didn't even look like it was raining, but my makeup artist would come in and she's like, 'You're covered in rain, your face is so wet. I don't know how we can't tell on camera.' It was so funny. But he's just the best sport, and it was a dream to have him on."

Harris credits original HIMYM director Pam Fryman with making sure everything turned out okay. "In true Pam Fryman form, she just carries on with a great postured confidence and helms the ship so well, and so given all of the strangeness of the circumstances, it just still felt like we were making good content," he says. "And weirdly, I would say 10 members of the How I Met Your Father crew, including the first assistant director, worked on How I Met Your Mother in similar job capacities, so I'm there playing a character that I haven't played for some time surrounded by the same voices and the same visages that I had worked with for almost a decade, almost a decade ago. All of it felt surreal, and exciting, and also business as usual. I loved to be a part of it."

Barney is the second original HIMYM character to pop up on HIMYF at a crucial point in Sophie's life — Cobie Smulders guest-starred in the season 1 finale as Robin to give Sophie advice on her love life. And it turns out that Smulders reprising her role is what set Harris' return in motion.

"I knew that Cobie got to play Robin in season 1 of the show," Harris says. "And I thought, 'Oh boy. Well, now this is inevitable. They're going to ask all of us.' Once Cobie does something, how can you say no? Everyone loves Cobie Smulders and she did a great job, and it was wonderful. So I thought, 'Well, I don't want to be the lone holdout, so I'll go second.' And thankfully Pam had reached out."

Patrick Wymore/Hulu

"I think this is all very strategic Pam Fryman: 'I'm going to go to Cobie first, then Neil can't say no,'" Duff says.

Harris agrees immediately, "Exactly, I don't doubt that's the case." But he notes that he didn't want to appear on the show simply for nostalgia's sake. "I talked with Pam and the gang and they pitched an idea, because there were slight reservations on how you want to bring back a character that is aged," Harris says. "In what direction do you want him to have aged? Is he worse, is he better, is he different, is he the same? What they had come up with was a smart call. And I was also excited to work with Hilary, so all of that seemed like it was a fait accompli in its own way."

But Duff admits that her nerves kept getting the better of her. "The first time that we ran lines together, Neil and I were in the hair and makeup room," she says. "It was just like he slipped into Barney, and I got a little flustered and I forgot all my lines. I couldn't remember any of my lines after that. It was a very exciting moment. Neil, you're so handsome, and you're so charismatic, and you're so freaking talented — I was just grinning ear to ear and it was super embarrassing."

Harris laughs as he remembers those first few takes. "That's very sweet, and ironically, you were forgetting your lines and then by the time we got onto set, you had memorized and learned all of your lines and I was constantly forgetting mine," he admits. "So it's nice, the yin and the yang of it all. We got there."

How I Met Your Father's two-episode midseason finale debuts Tuesday, March 28 on Hulu. Season 2 returns Tuesday, May 23.

Sign up for Entertainment Weekly's free daily newsletter to get breaking TV news, exclusive first looks, recaps, reviews, interviews with your favorite stars, and more.

Related content:

• The story behind How I Met Your Mother's most — wait for it! — legendary line

• How I Met Your Father showrunners break down that Lizzie McGuire cameo

• How I Met Your Father EPs break down Neil Patrick Harris' season 2 cameo: 'More is coming'

• How I Met Your Father creators on HIMYM callbacks and plans for season 2