The 30-year-old actress and Koma, also 30, adopted an older dog named Lucy on Thursday after getting back together in the fall.
Duff, whose dog Dubois died in February, shared a photo on Instagram of herself posing with Koma and Lucy on the street.
"Hey guys! We adopted an old dog," she captioned the picture. "thank you so much @lovelerescue #welovelucy."
Koma followed up Friday by posting a snapshot of himself with Lucy at home.
"I Love Lucy and she...looks fairly indifferent towards me. I will Ricky Ricardo her heart," the singer and DJ wrote.
Duff and Koma reconciled in October after splitting in March 2017 after a few months of dating. The actress discussed their relationship in an interview with The Talk in December, saying, "Timing is such a big deal!"
"I think that you have history and a past with someone and love, and just because it doesn't work out the first time, the second time, as long as there's not so much damage done, then it can always work out again," she said.