"You are the greatest -- ever!" Fallon said after Mirren appeared on the screen. "Oh my god. That is the greatest."
"I'm in my favorite place in the world," shared Mirren, who was surrounded by bubbles.
Fallon then pointed out that Mirren might be the first guest to appear on "The Tonight Show" while in a bathtub.
"Well, that's the brilliant thing about Zoom," Mirren replied. "I was thinking, you know, 'Why not be in the place that you love to sit and chat to people?' I love having a chat to my husband while I'm sitting in the bath, so why not do it to the whole of America?"
"That's very smart," Fallon told the star in response. "That's why you're the best."
However, Mirren -- who was promoting her new film "F9" -- hilariously joked that there's one issue with her bathtub interview.
"I'm running out of bubbles though, that's the problem," she quipped. "You're chatting away and my bubbles are going down."
"I'll make the interview very fast then," Fallon said, to which Mirren replied, "Fast please, fast and furious."
Meanwhile, "The Queen" star later shared what's keeping her from becoming an EGOT winner. Mirren has an Oscar, four Emmy awards and a Tony, however, she doesn't see herself winning a Grammy, at least not for singing.
"I have a terrible disadvantage where a Grammy is concerned, which is that I absolutely can't sing," she explained. "I mean, I really, really, really can't sing. So it's a terrible disadvantage for an effort to get a Grammy. Maybe I could do a spoken word album, but that's as close as I'm ever going to get to a Grammy."
Mirren went on to chat about the "Fast & Furious" and her character, Magdalene Shaw, AKA Queenie.
Fallon brought up how Mirren had asked star and producer Vin Diesel to let her join the franchise.
"I begged. I was shameless," Mirren hilariously admitted. "I begged, I whined, I moaned, I cried a little bit. I pulled every trick that I could possibly pull. And he very, very kindly acquiesced."
The "Good Liar" actress went on to star in "Fate of the Furious" and "Hobbes & Shaw." "F9" marks her third appearance in the car-racing film series.
Mirren admitted she had "begged to drive" in "Fate of the Furious" and "Hobbes & Shaw" and was finally given the opportunity to get behind the wheel in "F9."
The "Collateral Beauty" star also shared the meaning behind her character's name.
"My mom came from a big East End family. There were 14 kids in the family," Mirren explained. "It was a very old London family and I had an Auntie Queenie. It's a proper east end name Queenie so I thought that would be a good name for her to have."