This week, Arthur Cave would have turned 20 years old.

The son of iconic Australian musician Nick Cave died after falling from a cliff near Brighton, England, on July 14, 2015.

He was only 15 years old.

On Tuesday, Arthur's twin brother Earl celebrated the milestone birthday with his family.

"A birthday heart for our little Arthur," their mother Susie Cave shared on Instagram to mark the occasion.

Cave has been open about his exploration of grief following his son's death.

A documentary to avoid questions.

In 2016,One More Timewith Feelingdocumented the recording of Nick Cave and the Bad Seeds' 16th studio album,Skeleton Tree,after Arthur's death.

The documentary was Cave's idea, a way to avoid doing press for the album's release and having to answer questions about his son, director Andrew Dominik told The Guardian.

In the film, Cave said he doesn't want to escape from Arthur's death, but he doesn't want to commemorate him with platitudes and truisms, which people inevitably share following a tragedy.

"People say it all the time to me, 'he lives in my heart', and I go 'yeah, yeah I know' but he doesn't," he said.

"He's in my heart, but he doesn't live at all."

He said the grief had made it impossible for him to predict how he would feel and react to things.

"Now, I just don't have any handle on things any more... It's frightening because I don't know what I'm f*cking doing now, for example. What am I sitting in [front of] a camera, being filmed talking about this sort of thing? I wouldn't have dreamed of doing that before."

Dominick said the film, particularly the last scene, had a positive impact on the Caves.

Cave initially objected to footage of the cliff where Arthur died being used in the documentary, but after visiting the site with Susie the day after Arthur's funeral, Dominick decided to include it.

"When you stood at the top of the cliff and looked out, it was this beautiful view of the sea and the sky, something that suggested eternity, or continuum, or perhaps the insignificance of us all. I wanted to use it as a beautiful thing, as opposed to a horrible thing," he said.

"[Cave] has to drive past it, sometimes four times a day, because his studio is on the other side of town. He said he gets a feeling, like a constriction in his gut, every time he does.

"And Susie was unconsciously speeding up every time she drove by it; she didn't even know she was doing it, but she got caught on the speed cameras, she actually got fined.

"But he said that, since the film came out, he drives past there, and he gets a kind of warm feeling. I think that’s kind of beautiful, that the movie could have changed his associations."