Jimmy Fallon and Jennifer Lopez are writing a children's book together.

Jimmy Fallon is writing a book with Jennifer Lopez

Jimmy Fallon is writing a book with Jennifer Lopez

The 'Tonight Show' host - who has daughters Winnie, eight, and Franny, seven, with wife Nancy Juvonen - teased he has a "massive" project in the works with the 'Hustlers' star and joked they had settled on penning the story after the 'On the Floor' hitmaker rejected his idea for a duet.

He said: "The next idea we have... it involves JLo and it’s massive. We always wanted to do something together and, of course, me, I’m like, 'We should do a song together.' She’s like, 'No, I can’t. I’m busy. Oh, next time.'"

Speaking of Jennifer - who has Max and Emme, 14, with ex-husband Marc Anthony - he added to 'Entertainment Tonight': "We both have kids. She’s a great mom. Let’s think of something fun, a good children’s book, that we can get together and do something."

Jimmy teased the book will "help teach babies Spanish".

He added: "It’s really cute. The artist is great. I think people are going to really dig it. It’s a lot of fun."

While fans will have to wait for the collaboration, Jimmy has just released his new book 'Nana Loves You More' and he's very "excited" about the story, which reflects his own relationship with his beloved grandparents.

He said: "It's good, it rhymes, it's long enough to count as a book, but it's short enough where you can read it and go to bed... I’m excited about this one. Out of all the ones that I’ve written, this one's the closest to an actual real story. This is something you read at night to your kids. I’m excited about this.

"My grandparents on my mom’s side lived in our back yard... in a nice cottage. After school I would go over and they would babysit me. They helped raise me. They taught me how to cook, what music to listen to, [about] comedians... I got so much from my grandparents.

"If you’re lucky enough to have them in your life, it’s another way of learning from someone, from a different generation, to give you advice."

But he warned the book is "a little bit of a weeper" as it sends the message that "even when Nana’s not around anymore, you’ll always have her as a part of your life, you’ll never get rid of it, you’ll never, ever forget Grandma."

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