Castaignos, now 21, was a highly regarded youngster whilst with Feyenoord, making his first team debut as a 17-year-old, and in his first two seasons with the club he hit 15 goals - which subsequently attracted considerable interest from some of the biggest clubs in Europe.
It was Serie A giants Inter Milan who won the race for his signature, snapping the starlet up for just €3m. However, after just one season at the San Siro, Castaignos was flogged back to Holland with Twente, who rescued him from his Italian nightmare. 27 goals in 65 games have followed, and it appears he has now rebuilt his country - much to Swansea's delight.
The Swans have had a £6.5m offer accepted for the striker, but whilst their supporters may get excited about the deal, it could make for grim reading over the future of star striker Bony.
The Ivorian was a roaring success in his first Premier League season since arriving from Vitesse Arnhem for £12m a year ago, hitting 18 goals in all competitions and effectively keeping Garry Monk's side in the top flight with his goals.
But his deadly finishing has attracted the interest of Premier League rivals Arsenal, who are seeking striking help for Olivier Giroud after the Frenchman struggled to carry the workload on his own - and the news of Castaignos' expected arrival at the Liberty Stadium could be a huge boost to Arsene Wenger's side.
If Castaignos is seen as the replacement for Bony, then Arsenal will be lurking with intent for Bony, who is valued at around £20m by the South Wales club. The two aren't exactly like-for-like replacements given that Castiagnos' game is predicated on his movement whilst Bony is a more physical presence, but Swansea would simply be looking to replace the goalscoring output of their star striker.