Radcliffe was game to voice the character Gary Potter - Harry's cousin - in the new film, but Mike Mitchell decided it would be a bad idea to poke fun at the boy wizard.
"Gary was an unlicensed character. He didn't make it in," the filmmaker explained to Entertainment Tonight. "We were definitely going to go out to Daniel, and he was game, but unfortunately his character got cut."
"I don't remember why it happened. I think it was because we didn't want to upset any 'Harry Potter' fans. They have such a following, so we decided to upset the 'Mary Poppins Returns' fans (instead). We just made Larry Poppins."
There are still plenty of voice cameos in the film, popping up alongside stars Chris Pratt and Tiffany Haddish - Jason Momoa and Gal Gadot represent their superhero characters "Aquaman" and "Wonder Woman" and even top U.S. judge Ruth Bader Ginsburg shows up.
"We just decided, 'Who would be not only the strangest person to invite to the wedding (scene), but a really fun person to add to the wedding?'" Mitchell said, "We're like, 'Ruth Bader Ginsburg. Why not?'"
Bruce Willis also appears in the sequel: "I thought that was pretty great, that he was willing to poke fun at himself," the director added.
And Momoa was on board before he was even invited to be part of the "Lego Movie" sequel: "Jason Momoa was ready to go before we were even ready to go," Mitchell laughed.
"Just to dip our toe in the water, we did a little Comic-Con piece... and Jason made an appearance just because it was going to be showed at Comic-Con. So Jason came in and right away just started embracing that character as crazy as he is. He kind of created that character, and we're like, 'That was so great, let's pull that into the movie'."
The new "Lego Movie" opens in theatres next month (February 2019).