Gwen Stefani knows a blood relationship isn't necessary for a man to be a good father.

The singer posted a tribute to her fiancé, Blake Shelton, on Sunday, wishing him a happy Father's Day.

She also uploaded a series of images of Shelton with her three sons -- Apollo, Kingston and Zuma -- whom she shares with her ex-husband, rocker Gavin Rossdale.

"happy father's day to the most generous patient loving funny guy i know - we love u so much," she wrote.

This post comes just a few days after the country singer turned 45, and Stefani surprised him with a birthday bash.

"celebrating my besties b day today love u @blakeshelton" and hashtags including "#favoritecountrysinger," she captioned videos from the celebration.

In the clip, guests gathered in the backyard shout "surprise!" when Shelton reaches the back doorway. Stefani, who's close behind him, can be heard saying, "It's your birthday," after Shelton seems to think the surprise is for someone else.

A second clip shows guests, including someone dressed up as Superman, singing "Happy Birthday" to Shelton, before the DJ cuts to 50 Cent's hit "In Da Club."

Stefani, 51, also included a cute snapshot of the couple kissing in her post.

Stefani and Shelton confirmed their relationship in November 2015, after meeting as co-judges on "The Voice." They announced their engagement in October 2020.