While filming her scenes for the sci-fi sequel, Winslet held her breath for an incredible seven minutes. She shattered the record previously set by Tom Cruise for an underwater scene in Mission: Impossible - Rogue Nation, in which he held his breath for six minutes.
However, as Winslet told ET's Nischelle Turner, she didn't even know that her record was public knowledge.
"It's so funny because I don't really read reviews or media things. I'm not on Instagram, like I'm just completely disconnected from that part of my life," she explained. "So all of this week and the week before, I've had people coming up to me at work saying, 'Oh my God, like seven minutes and 14 seconds? Like, what?!" And I'm going, 'What? Hang on, wait a minute. How do you know that?'"
"It was brilliant and I was very proud of myself and I'll probably never be able to do it again," Winslet added. "That came at the end of four weeks worth of quite intense training and it was in the dive tank, it was in the training tank. But I loved it."
As Winslet explained, it's doing new and unexpected things that has proven to be "one of the things I love about the job."
"We're very, very lucky as actors that often we have to learn a whole new skill," Winslet shared.
The actress was joined for her interview by Saoirse Ronan, with whom she shares the screen in director Francis Lee's acclaimed period drama Ammonite. Winslet explained that her role in the film also provided the opportunity to learn a whole new set of skills and knowledge.
"I had to learn how to be a paleontologist on the beaches of the Jurassic coast on the south coast of England," Winslet shared. "I had no idea how to do any of those things, and sometimes the job does require us to learn how to do something new, something incredibly cool."
For Ronan, it seems that working with Winslet was the coolest part of the project.
When asked about how hard it was to keep her cool around Winslet -- considering Ronan is a massive Titanic fan -- the 26-year-old actress admitted, "It's hard. Because Kate is so cool. Kate is such a cool, cool, cool chick."
Ronan recalled how she was shooting Little Women when she first read the Ammonite screenplay, and was shooting a scene with Timothee Chalamet where they are ice skating together, which reminded her of one of Titanic's iconic romantic scenes between Winslet's Rose and Leonardo DiCaprio's Jack.
"It's like a carbon copy of the famous shot in Titanic, and I said to him, I was like, 'This is our Jack and Rose moment!' And then I went back to my chair and got my phone out and Kate had called," Ronan remembered. "I was like, "I've just done your shot! Oh my God, we have to do this film together!'"
"I had a few films throughout my childhood that I would watch religiously, literally every single night, and Titanic [was one of them]," Ronan added with a smile.
While the love story of Rose and Jack has become an indelible part of pop culture, there's a growing fandom for another one of her romantic tales, The Holiday, which is celebrating the 14th anniversary of its release on Nov. 29.
"For me, the biggest take home, honestly, was working with Jack Black," Winslet said, reflecting on the heartfelt rom-com. "We really had a lovely time together. He's just a sweet, generous person and I hadn't worked with him before... it was a very special time working with him."
"Also, Eli Wallach, who sadly is no longer with us," she added. "He turned 91 when we were making The Holiday, and he would tell stories about what it was like to dance with Marilyn Monroe and I would just hang on his every word, and that was pretty special."
Winslet and Ronan's romantic drama Ammonite hits theaters Nov. 13.