After two golds and a bronze there was neat symmetry to Simmonds's second place as Arlen, her equally prodigious fellow 17-year old, took the title with an impressive swim.
Simmonds now has six Paralympic medals of every hue and it’s a collection she has every intention of adding to, while her rivalry with Arlen could be a duel in the pool to enjoy for many years to come.
Simmonds was quick - posting the fourth fastest time in history - but Arlen, three times a silver medallist, was even quicker, bettering her own world record, which she equalled in the heats, and clocking 1:13.33.
“I would have loved to have got that gold medal but you can’t have everything,” said Simmonds, who won the 400m freestyle and 200m medley, plus 50m freestyle bronze, earlier in the Games.
“Silver is really good, I went out there and I did the best that I could and I took over a second off my personal best.
“I have got two gold, a silver and a bronze and I have broken four world records, I couldn’t have asked for a better competition.
“I’m just really chuffed with how I’ve performed here, there was so much pressure and expectation but I think I’ve coped with that well. Nothing can prepare you for competing at a home Games, it’s just been an amazing experience.
“Victoria is great, she is pushing me to my limit and that’s really exciting. We’re both the same age and it’s such an exciting rivalry for the future. Next year’s World Championships are going to be really good and by Rio hopefully we’ll both be swimming even faster and maybe others will be challenging too."
Like Simmonds, Arlen - whose Games started by being effectively told she wasn’t disabled enough to compete - is a class act, although for those seeking headlines this appears a genuine friendly rivalry, with the pair swapping swim hats and gossiping as they waited backstage to collect their medals.
"Everyone says we're enemies but we're really good friends and we’re really pushing each other," said Arlen.
"She's been an amazing inspiration to me and I love racing against her. We are only going to keep going at it and keep pushing each other to drive these world records down.”