Miley Cyrus Boyfriend, Cody Simpson flaunted his muscular biceps as he debuted a new song

Australian singer Cody Simpson joined forces with Bonds Australia to launch a special hoodie for Earth Day.

The 23-year-old took over Bonds Instagram Live on Wednesday for the launch, where he debuted a new song he'd written called Castle Walls.

Appearing from his home in Los Angeles that he shares with girlfriend Miley Cyrus, Cody flaunted his bulging biceps and tattoos in a grey chesty singlet from Bonds.

'I'm going to sing you a couple of tracks that were inspired by my desire to preserve the planet,' he said while sitting on the couch, holding a guitar.

The Gold Coast-born singer then launched into an acoustic version of his hit 2015 song Wilderness, before reading several poems from his new book Prince Of Neptune.

Cody then went onto debut Castle Walls, which he said will be the next song he releases.

The launch was in aid of Bonds Unisex Earth Day Pullover Hoody.

The special limited edition sweatshirt is made with reclaimed fibres and undyed and is available online for $74.95.