Switzerland's Jeremy Desplanches was the surprise winner in the men's 200m medley, not just to his rivals, but to himself too.
"What he did tonight is amazing," said 23-year-old Bonnet, who won her gold by 1.77 seconds from Dutchwoman Femke Heemskerk.
"He told me he didn;' believe he could win. I was even more moved by seeing him win than for my own gold medal. I'm so proud of him. We train together, we live together, we share everything."
Bonnet, a relay silver medallist at the London 2012 Olympic Games, had already won a 4x100 freestyle relay gold at these Championships. She led all the way to finish clear of Heemskerk and Russia's Anastasia Guzhenkova (RUS).
Desplanches edged clear of Germany's Philip Heintz. The bronze medallist was Max Litchfield (GBR), who was returning to action in Glasgow after a year marred by injury.
Desplanches said: "In the call room, I was sitting when Charlotte was swimming. Halfway through the race, I knew she was going to win. It was hard to restrain myself, not to jump around.
"She told me before the race, 'When I swim, keep calm'. I’m really proud of her. Charlotte's win gave me a boost. It gave me wings for sure."
Outstanding Russian teenager Kliment Kolesnikov helped his team to take a firm grip on the swimming medals table.
Kolesnikov, who was 18 in July, has raced on all four days and will be in action on Tuesday and Wednesday too, in the 200m backstroke. He has three golds, a silver and a world record to his name so far.
He took the 100m backstroke in 52.53 seconds, a personal best and the second fastest time in the world this year, then helped Russia to a silver in the mixed medley relay behind Great Britain, who set a European record.
Russia had another gold when Anton Chupkov (RUS) beat James WILBY (GBR) in the 200m breaststroke with a European record time of 2 minutes 06.80. The third-placed Italian Luca Pizzini (ITA) touching a hundredth of a second ahead of the fast-finishing Ross Murdoch (GBR).
"I would have broken my hand to get a bronze medal," said Pizzini.
Hungary's Boglarka KAPAS surprised herself and her rivals when she won her first senior non-freestyle medal, the 200m butterfly, ahead of Svetlana CHIMROVA (RUS) and Alys THOMAS (GBR). She started taking the butterfly seriously only six months ago.