Kate Walsh Reflects on the 'Fever Dream' of Reuniting on 'Grey's Anatomy' With Ellen Pompeo

The actress also discusses Thursday's new episode.

Kate Walsh's return to Grey's Anatomy marked a blast to the past, reuniting her with Ellen Pompeo and reintroducing her beloved character, Addison Montgomery, back into the medical world. While last Thursday's episode only marked the beginning of Walsh's journey back in the halls of Grey Sloan Memorial Hospital, stepping back into Addison's stylish high heels was, as the actress reveals, a daunting task.

"It was surreal. It was like a fever dream. There's so many different things coming together and it's impossible to describe," Walsh told a handful of reporters, including ET, over a recent Zoom call when asked about her return. "Randomly, I had run into Patrick Dempsey on the plane on the way back from France, like a month before I was coming to do the show and I told him I was going to come back and he'd said, 'It's going to be so intense for you. And so emotional and so many feels and then closure too.' When we started that show, it was such a specific time for all of us and the entire cast. It really changed every single person's life in a pretty dramatic way."

"It was so massive to go back and try to process all of that and then have the younger actors that are playing the interns, who were so beautiful... They were like, 'Oh my god, I watched Addison with my mom!'" she recalled. "And also to be reunited with Jim Pickens and Chandra [Wilson] and Ellen. Those are the three that are the originals. I didn't get to see beautiful Kim Raver because our schedules were completely opposite. So we just texted, but I love her and Kevin [McKidd], I got to see for a second, I think, because he was directing another episode, and Chandra and Jim and Ellen, that was really, really meaningful and powerful."

"We were going through pictures. Chandra had on her tablet, our press photos from when we went and did press in Brazil. I don't even know what it would've been, like 2006 or 2005? It was when her now teenage son was a baby. It's a lot," Walsh acknowledged. "It was really beautiful, but a lot. So it's impossible to articulate I think. But I will say, I think all of that went into the episode acting-wise and it was easy to show up emotionally and all of a sudden get cracked open in the elevator because there's just so much."

Eric McCandless/ABC

The emotional elevator scene between Walsh's Addison and Pompeo's Meredith, once antagonists, was emblematic of how far the two characters' complicated relationship has come over the past two decades. In the heartbreaking scene, Addison breaks down in tears over the void she felt was left by Derek Shepherd.

"When we read it, the first time I saw the script was... a Zoom table read and I was so thrilled with it and when that scene came, it was like I was reading it cold and it was so moving because I'm like, 'How the hell am I going to deal with that? She didn't even come to Derek's funeral.' How are we going to sort that out?" Walsh said. "I thought the writing was so beyond. And you know, my friend, Jamie Denbo... she wrote it in such a sophisticated way: 'I thought that he'd be here.' It's so not what you'd expect. It's so tangential, it's so not how she's feeling. It's not on the nose. It was so beautiful."

"One of my other friends who works in post was talking about it, just that specificity of the writing in that moment was so good. And I just loved it. And Ellen is just awesome because we're two people who literally up and through rolling are just gabbing and then you stop and then go into the scene. She's literally telling me, 'Oh, this is where you could get your smoothies from. This is where you should go eat.' And then, 'Action,'" Walsh continued. "There's this strange thing that happens where you're there. It's like a little warm hole that you go into. That's what makes it a fun ride because she's been playing Meredith for so long now and the beautiful thing is, as long as you know the lines, you just go and see what happens. Neither of us knew what really was going to happen. There are markers. What they wrote was Addison goes from laughing to crying, and then you get to interpret that and hopefully it works. I'm glad that it [did]. It felt right. It felt wildly uncomfortable and weird, and I think that's exactly what it was -- and vulnerable. And when Meredith goes to give her a little embrace at the end, these things aren't written. That's the beauty of being able to do this stuff. So I hope that you all liked it and enjoyed it."

When Thursday's episode rolls around, Addison's storyline is slightly more self-contained and involves her former Private Practice colleague, Amelia (Caterina Scorsone). 

"You really see Addison and Amelia's dynamic play out. They're reconnecting and that was a total delight for me, and I think fans will enjoy that as well. It's a completely different kind of episode than the first one, but intensely intimate and satisfying," Walsh teased. "I remember Krista saying that they wanted to keep it Grey's and not Private Practice, in the sense of what the dynamic is of Grey's Anatomy and the hospital and making sure it's framed around medical cases. All of the personal stuff that transpires is really still framed around these life-and-death moments. What's going on with Tovah, the patient. That's the kind of magic, I think, of Grey's and what Shonda originally created that is still going forward. Why it's still so successful is that it is all framed within this very heightened, contained combustible space of the hospital and these life-and-death moments. And with that, I should say that the personal transpires."

Grey's Anatomy airs Thursdays at 9 p.m. ET/PT on ABC. For more, watch below.

To stay up to date on breaking TV news, sign up for ET's daily newsletter.