The singer-actress was out in the posh 90210 area running errands and getting her nails done when she walked by eatery Nate 'n Al, where the 22 Jump Street actor had been dining.
Hill exited the restaurant as Duff was passing. According to photographers, Mike Comrie's ex called out his name but wasn't able to grab his attention in time and he unknowingly continued on.
The mom to son Luca, 2, looked effortlessly chic in a white tank dress. She, too, proceeded with her day, grabbing a green juice and enjoying some pampering at Beverly Hills Nail Design.
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!