Shane Geraghty never managed to inspire Saints to victory at Welford Road, but that was exactly what he did for London Irish last weekend.
The blond-haired fly-half kicked 17 points as the men from the Madejski Stadium secured a surprise 22-19 success at Leicester.
Geraghty will now set his sights on toppling former club Saints, who he left in the summer of 2012.
And his former boss, Jim Mallinder, has been impressed by the development of a player who hit the heights at Northampton before falling out of favour.
“(London Irish boss) Brian Smith has put a lot of trust in him,” said Mallinder. “He’s matured and he’s playing well.
“He’s always been a good passer of the ball, he’s always been an elusive runner, he looks to be kicking the ball well from restarts and at goal so good luck to him.
“He’s playing well and he’s somebody we really need to watch at the weekend.”
Stephen Myler eventually ousted Geraghty, who had won England honours during his time at Saints, but the 28-year-old has bounced back well.
He was the star of the show in Irish’s defeat at the Gardens back in April and has made the starting shirt his own.
“He probably has developed, he’s matured,” added Mallinder. “Quite a lot of that comes from playing more games.
“At Irish he’s been starting most weeks and he’s played at 10 and 12. When you’re starting every single week it helps.”