Cate Campbell's wonderful gesture for winning sister Bronte

Moments after being pipped to the gold medal by sister Bronte, Cate Campbell showed her class with a beautiful act of sportsmanship on Monday night at the Commonwealth Games.

Bronte upstaged her big sister and favourite for the 100m freestyle crown, with a blistering comeback to claim the gold medal.

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The winning time of 52.27 seconds by the younger of the Campbell sisters was the fourth-fastest time in the history of the event, relegating Cate to silver in a very fast final.

But any hint of disappointment from Cate was quickly dispelled in a beautiful pre-race moment that will live long in the memory of fans.

Grabbing her sister's arm and hoisting it high into the air in triumph, it was obvious there was no sibling animosity as Cate celebrated Bronte's victory harder than just about anyone else poolside.

Both women were grinning from ear to ear and you could tell Cate was over the moon for her little sister.

Bronte, who has spent even longer in the shadow of her acclaimed sibling Cate, said was shocked to claim gold after the race.

"That was incredibly surprising," she told the Seven Network.

"I don't know how that happened but I am glad it did."

Bronte said she would now take an extended break from swimming before the Tokyo 2020 Olympics.

"I am getting held together by sticky tape," she said.

"I made a decision to have a break after this ... the break is going to have to happen if I want to do another two years, which I do, all the way through to Tokyo."

Making Bronte's victory even more interesting was the fact it may have bumped Cate out of Australia's medley relay team.

Cate appeared a lock for the freestyle leg of the medley final on Tuesday's last night of the swimming after her triumphant return from her own 2017 sabbatical with three gold.

But the jury is now out.

"I was 100 per cent going out there thinking 'his was my last race for the meet and the year," Bronte said.

"I was saying 'this is my last warm-up, this is my last suit' before the race.

"But I might have to do the relay now. We will see how we go."

Cate may yet jag the freestyle leg after her remarkable 51 second flat effort that anchored Australia's world record breaking 4x100m freestyle gold medal win on the Gold Coast.

"Cate did an amazing split in the relay so if she did the relay I would be stoked," Bronte Campbell said.

Cate said the national selectors' final call on Tuesday may come down to a round of "paper, scissors, rock".

"If I don't have to swim I get the night off and will cheer in the stands," Cate Campbell said.

"If I do swim I get to swim for my country so they are both wins in my book."

With agencies