Robert Downey Jr.'s son Indio Downey is celebrating the actor's latest life milestone by sharing a nostalgic childhood photo.

The Oppenheimer star turned 60 on Friday, April 4, and Indio marked the special occasion with a touching tribute to his dad on Instagram. On Saturday, April 5, Indio, 31, shared a set of photos of the duo — a recent shot of them posing together at an industry event and a throwback snap of himself as a young boy, planting a kiss on Robert's cheek.

In the black-and-white image, Robert wears a white T-shirt with the word "Brat" printed across the front, while Indio holds his tiny hand against his cheek.

Indio captioned the birthday post: "It’s the big 6-0 for the legend @robertdowneyjr! happy birthday dad 🖤 you’re the best."

Robert shares Indio with ex Deborah Falconer. He is also dad to son Exton, 13, and daughter Avril, 10, with his wife Susan Downey.

Related: How Robert Downey Jr. Is Preparing for His Marvel Comeback as Doctor Doom: 'It's a Very Intense Process'

Ahead of the January 2024 release of his debut EP, Cigarettes in Bed, Indio opened up to PEOPLE about how his father encouraged his love of music at an early age.

“My dad actually really inspired me to play music when I was young,” said Indio, who shared that he got his first guitar at 12 years old.

“He sings, and he has an album as well that I listen to a lot," he added of Robert. "I was very fortunate to grow up in an artistic family, which allowed me to develop my creativity and my talents.”

Robert is currently prepping to return to the MCU as the villainous Doctor Doom, after years of playing beloved hero Iron-Man.

Co-directors Joe and Anthony Russo shared how seriously Robert is taking his Avengers: Doomsday role in an interview with Entertainment Tonight on March 4.

"It’s a very intense process developing the character," Joe said. "He’s so immersed in it. He is so dialed in."

Related: Robert Downey Jr. Is 60! See Him in Dad Mode in These Rare Photos with His 3 Kids Indio, Exton and Avri

According to the Russos, Robert has gone as far as "writing backstory [and] costume ideas" for the villain. "I think he just loves really rich, three-dimensional characters, and I think he sees a real opportunity here with that character," Joe added.

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