Jake Gyllenhaal Jokes He's Not Speaking With Ryan Reynolds After Best Friends Day Feud (Exclusive)

The actor also raved about co-star Tom Holland's acrobatic skills in 'Spider-Man: Far From Home.'

Jake Gyllenhaal is joining the Marvel Cinematic Universe in Spider-Man: Far From Home -- but he's already got some famous friends to show him the ropes of the superhero life.

"I loved the first movie of this franchise. I mean, I thought [director] Jon Watts had created a tone, and it was funny, it was moving, and I really liked that about it," the actor explained when he and co-star Samuel L. Jackson sat down with ET's Keltie Knight in London to discuss the upcoming Marvel film. "And I thought Tom [Holland] was an incredible Spider-Man."

"I was a little worried about the fish head thing," Gyllenhaal admitted of the costume for his character, Mysterio, "but ultimately, the suit is sick, and that was that."

Gyllenhaal got some practice with his "fish head" helmet ahead of filming, he explained -- and even got to take one home and snap a hilarious Instagram pic with it over breakfast.

"That was the helmet that I practiced and trained in," he explained of the pic. "After I learned how to fly, one of the things that I wanted to make sure of was that I could fly with the actual fishbowl on my head, so Marvel gave me one, and then also I filled it with smoke and would fly around with it on my head and it worked. Then I was ready to make the movie."

"You're doper than Ryan, because he can't fly," Jackson chimed in, referring to Gyllenhaal's ongoing social media "feud" with pal Ryan Reynolds. The pair recently posted pics in honor of National Best Friends Day on June 8 -- but conveniently, and hilariously, left each other out of their respective shots -- posing instead with mutual pal Hugh Jackman and noting the other as "not pictured."

"I used to talk to him a lot until a couple weeks ago, so I wouldn't really know what's going on," Gyllenhaal teased of Reynolds' reaction to his joining the MCU.

When it came to a debate over the "Sexiest Avenger," Gyllenhaal and Jackson had a hard time landing on a favorite, however, both admitted to how impressed they were by Holland's performance as Spider-Man, particularly when it came to the young star's acrobatic physicality.

"I mean, one of the first scenes I did in the movie, I'm laying on the ground at the end of this battle, and he's supposed to enter. That's how it was written, but instead when I got to set, there's a trampoline on set and the dude jumps on the trampoline, does two backflips and lands on his hands and feet like Spider-Man, and then starts the scene," Gyllenhaal recalled. "I was like, what's going on? I couldn't conceive of that kind of physicality in an actor... He's incredible, like, the physical stuff he does is incredible."

That's not to say that the Nightcrawler star doesn't have some impressive skills of his own. Gyllenhaal recently showed off his singing skills during a surprise appearance on The Late Late Show With James Corden in London, where he teamed up with the talented host to perform a parody of Whitney Houston's "The Greatest Love of All," titled "The Greatest Gyllenhaal of All."

In the silly song, Corden starts out by singing Jake's praises, but Gyllenhaal eventually admits in his verse that "the greatest Gyllenhaal is actually Maggie," his older sister.

"They asked me if I would sing 'The Greatest Love of All' with James Corden, and obviously I said yes immediately," he recalled of how the bit came together. "Then they said they were changing the lyrics to 'The Greatest Gyllenhaal of All' and that was literally that. We performed it twice and I was in over my head. The truth of the matter is that there are a lot of Gyllenhaals, but Maggie is the best, as she has always been. I'm the younger sibling."

Spider-Man: Far From Home swings into theaters on July 2. Check out ET's trailer breakdown below!