Naruto apparently didn't hide his wince when Boruto called him "father" well enough, because his boy who was now a ninja had spotted the tiny, near invisible tell.

"What is it dad?" Boruto asked, looking like he almost feared the answer.

"Well, I guess you're old enough to know now." the Nanadaime hokage replied, setting aside his ever-present paperwork.

"Know what?" Boruto asked, looking somewhat scared.

"Well, since you and Himawari took after Hinata in certain ways, I didn't think you needed to know about the Namikaze Kekkei Genkai, or..." Naruto said. "But, well, it's better you hear this from me than some random villager."

"What are you talking about dad?" Boruto asked.

"Son," Naruto said. "I'm not your father."

13 Years Earlier:

"Just a little more, and push." Sakura said to the woman on the bed who was giving birth.

Naruto, who lay on the bed gasping and panting turned to his, er her, beloved wife and said "I don't know how you did it, and frankly I don't care right now, but you're carrying the next one!"

Present Day:

"...and, so, Hinata's actually your father, and I'm really your mother." the Nanadaime Hokage said, choosing not to notice the utter horror on his son's face, and the fact that the boy was absolutely green around the gills.