Pompey will receive a £500,000 windfall if Stoke remain in the Premier League this season.
That is the result of an add-on agreed as part of the Marc Wilson deal back in August.
At the time, the Blues received £1.5m from the Potters, along with Liam Lawrence and Dave Kitson, in exchange for the Irishman moving to the Britannia Stadium.
The News can reveal that an extra clause was put into the deal to give Pompey an extra £500,000 if Wilson helped the Potters achieve top-flight safety.
Since his move, Wilson has gone on to become an integral part of the Stoke side who have reached the FA Cup final.
That deal has proven to a bargain for the Blues, with Lawrence and Kitson helping to comfortably keep them in the Championship.
Now Pompey stand to receive an additional £500,000 if Stoke, as expected, avoid relegation from the Premier League this season.
Once the Potters are mathematically safe, Pompey expect to receive the windfall.
Wilson has played 29 matches for Stoke so far, scoring one goal, with his versatility proving priceless.
He has recently been operating at left-back and was part of the side who destroyed Bolton 5-0 in the FA Cup semi-final to book a Wembley date with Manchester City next month.
The 23-year-old is now in line to be part of an FA Cup final squad for a second successive season.
However, Wilson will hope to play a part this time after missing out playing for Pompey against Chelsea last year because of a hamstring injury.