“3 years buddy! 3 beautiful years! You make every minute worth while! We cherish all your firsts and all that is to come,” she wrote. “Happy 3rd birthday my love #timesflying #whatayear.”
The 27-year-old included her soon-to-be ex-husband Mike Comrie in the Flipagram pics, which show Luca enjoying time in the sun and snow with both his mom and dad.
Duff and Comrie, 34, announced their separation after five years of marriage in January 2014, and the actress and singer reportedly filed for divorce in February 2015, shortly after rumors swirled about the former NHL player having a wild night out with friends in Beverly Hills, California.