Australian swimming champion James Magnussen's fiancée Rose McEvoy shows off her huge diamond ring as they step out together in Sydney

Australian swimming champion James Magnussen and his new fiancée Rose McEvoy stepped out together in Sydney on Saturday.

The Olympic medallist, 33, and the glamorous blonde put on a loved-up display as they went for a stroll in Double Bay.

Rose showed off her huge diamond ring during the outing, as she walked alongside her beau.

Onlookers also got a glimpse of the sparkling ring as she packed her phone and other items into her handbag.

Rose looked stylish for the outing in a brown halter-neck top, loose white pants and a pair of brown sneakers.

She left her long locks out and left her natural beauty shine with a neutral makeup palette.

James also dressed casually in a green buttoned shirt, beige shorts, and a pair of sneakers.

The swimmer proposed to Rose in August, just weeks after wrapping up work on the Olympics in Paris.

Rose took to social media at the time to share intimate footage of the proposal.

'For the first time in my life, I was speechless,' McEvoy wrote on a shared Instagram post, including a video of the moment Magnussen got down on one knee.

'You can assume it's a yes. James Magnussen I love you more than words can describe.'

The giddy couple could barely contain their excitement as they embraced on a floating wooden dock, while Magnussen waited for a friend to capture the special moment which took place during a holiday at Hvar Island in Croatia.

McEvoy looked genuinely stunned as she turned towards her partner, expecting to pose for a video rather than have a ring put on her finger.

'If you push me in (the water) I'm going home,' McEvoy joked before 'The Missile' quickly knelt down and pulled a ring out from his pocket.

'I love you, will you marry me?,' the ex-swimmer said as McEvoy held back tears and family and friends surrounding the couple cheered.

The model and actor's jaw dropped and she stumbled slightly at the question, turning towards their friends with her mouth hanging open in a shocked grin.

Magnussen had to tug at his partner's arm gently to remind her to answer the question.

The lovebirds later shared the joyous news with their friends, with McEvoy flaunting the giant diamond ring.

Magnussen and McEvoy have been dating for 10 years and met when Magnussen was a 23-year-old Olympic freestyler and McEvoy was a 21-year-old law student and part-time model.

The first reports of their union surfaced in 2014 when McEvoy uploaded a a picture of herself cuddling up with her beau on her 21st birthday.

'Celebrating my 21st birthday with my beautiful man ! Thank you to all my wonderful friends and family who spoiled me and made it a fun night!'

Meanwhile Magnussen, who had once claimed that having a woman in his life would only distract him from swimming , won gold, silver, and bronze medals at the Olympic Games in 2012 and 2016.

The adorable couple are said to have first met through mutual swimming acquaintances along with the help of her father, who is a prominent physiotherapist.