The 40-year-old actor and the model have six-year-old son Flynn together, and despite divorcing in 2013 - three years after tying the knot in 2010 - they have remained close in order to successfully co-parent their son.
Taking to Instagram in celebration of the brunette beauty's 34th birthday on Thursday (04.20.17), the 'Pirates of the Caribbean' star shared a photo of a sweet handmade sign seemingly made by Flynn, which read "I [love] u mum" displayed in wooden sticks.
Orlando captioned the snap: "#HAPPY BIRTHDAY to an amazing mother co-parent and friend (sic)"
Previously, the 'Troy' actor - who recently called time on his romance with pop megastar Katy Perry after a year of dating - admitted that watching his son being born had a "profound effect" on him as a person.
He said: "No single moment has had such a profound effect on my life as when I held my son after his mother had endured 27 hours of labor.
"That should teach any man the meaning of respect for mothers the world over."
And the 'Kingdom of Heaven' actor also believes becoming a father has made him a more compassionate man.
He said previously: "Being a father, you know, you kind of have a new sense of responsibility. [My] level of compassion has grown."
Whilst Orlando has recently re-joined the single life, Miranda - who is engaged to Snapchat founder Evan Spiegel - recently claimed her wedding plans were "coming along" nicely.
Asked about wedding plans, she teased: "It's coming along, that's about all I can say. It's very exciting."