Donald and his wife CaCee Cobb welcomed their little son Rocco into the world back in August and given Donald's close friendship with his former co-star, the new parents announced Zach as godfather.
And the Scrubs main man (who played physician JD) appears to be loving his new role in Rocco's life.
On Wednesday (11 December), Zach tweeted: "Me and my god son. Made with @donald_faison's sperm" along with a super cute picture of himself holding Rocco in his arms.
The four-month-old has even cracked a smile for the camera and just look at those gorgeous chubby cheeks!
Zach and Donald (cast as surgeon Turk) have remained good friends since leaving Scrubs back in 2009.
In fact, the pair are such BFFs that Donald wed CaCee in an intimate ceremony held at Zach's home in Los Angeles last December. Aww!
Also in attendance at the couple's winter wedding was CaCee's best friend Jessica Simpson, who gave birth to her second child Ace Knute just two months before CaCee had Rocco.
Meanwhile, 38-year-old Zach struck up a brand new bromance last week with our very own Harry Styles!
The One Direction star was pictured having a candlelit meal with Zach during a whirlwind trip to the States.
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