Fun in the sun: Robert Downey Jr was seen on the beach in St Barts on Sunday

Doting: He was seen playing with son Exton Elias as wife Susan looked on

Looking in great shape the Tropic Thunder actor wore a pair of navy floral board shorts and a necklace to complete his surfer dude look.

Making sure Exton Elias, who was born in February of 2012, didn’t get burnt he was dressed in a blue rash vest and shorts.

Robert, who also has a much older son Indio from his marriage to Deborah Falconer, was seen helping his son build a sandcastle – going back and forth to the water to fill up the buckets for him.

Let’s dig: Susan and Robert helped their son build a sand castle

Lots of laughs: Susan couldn’t help but smile as she watched the men in her life play

Hanging out: Robert refreshed with a bottle of water while his wife held on to their son

At one point they headed into the sea to cool off – with Robert carrying his son in his arms.

After awhile Robert slipped on a bright orange hat and T-shirt, so he too didn’t get burnt, while his wife kept covered up in a pretty paisley summer dress.

The pair who met on the set of Gothika in 2003 married in 2005 and Robert famously credits his wife with helping him kick his drug and alcohol addiction.

Covered up: Robert made sure his son didn’t get burnt by dressing him in a rash vest and shorts

Ready for action: Robert made his way into the water, going unnoticed amongst his fellow beach goers

‘The old saying is true — behind every good man there’s an incredible woman,’ he said. ‘I owe a huge amount — if not all — of my success to Susan.

‘We make a great team, and all that luck I spoke about, that’s Susan’. he gushed about his other half.

In 2008, Robert got his massive break by playing Tony Stark in the hit Iron Man, which has led him become the highest paid actor paid actor in Hollywood with estimated earnings of £45 million.

Under he goes: Robert submerged himself into the water

Splashing about: The actor wore a necklace around his neck – creating a surfer look

The water’s good: The actor gave a thumbs up as he went swimming

And things only look set to get better for him as he will next play a fired chef who reinvents himself as a food truck owner in Chef, which also stars Sofia Vergara and Scarlett Johansson.

And his upcoming movie, The Avengers: Age of Ultron, is slated for release in 2015.

Come on in: Robert seemed to gesture to his wife to come in the water

Helping out: The actor was more than happy to run back and forth to get more sand

Bright and bold: Robert wore a bright orange T-shirt and a cap once he was out of the sea