"Quite the milestone today … as my magnificent daughter Estella @dinniganwilkins turns 18!" the 68-year-old captioned the snap, adding, "Happy Birthday my Darling … so proud to be your Dad .. and so excited for what the future holds for you! The stirrups of the world are at your feet !! All my love … X♥️X #StellsBells"
Estella replied to the sweet gesture in the comments, writing, “Thank you papa. Love you.”
A slew of famous faces were among those to wish Richard's youngest daughter a happy birthday, including Melissa Hoyer who wrote, "Lots and lots and lots of birthday love Estella @dinniganwilkins - what a milestone – have the best best birthday week."
Rebecca Maddern added, "Beautiful xxx" while Jess Rowe sent a trio of heart emojis.
Richard is also a proud dad to sons Adam, Christian and Nick, and daughter Rebecca, whom he shares with four different mothers.
The TV host has previously spoken about his experience in becoming a dad at age 18 to eldest son Adam, 47, who has Down syndrome.
"I was only 18 when Adam was born [and] his mum was just 16, very unusual for Down syndrome people to be born to such young parents. It was a shock to be a parent let alone of a Down syndrome child," Wilkins told Today Extra hosts Sonia Kruger and David Campbell on World Down Syndrome Day.
"I'm prepared to admit that I wasn't the greatest Dad back in the day. I didn't really know how to handle it," he said, adding, "I was getting on with my life and career, I wanted to travel the world and make music and do that sort of stuff, and it was with some reluctance that after about a year we put Adam in a home.
"People said you can have him adopted. But I said 'No he is always going to be my son' and I want a relationship with him. He has had great people in his life over the years."