The 22-year-old impressed at both centre-back and at right-back, featuring in every game during his loan stint and amassing 22 appearances.
And his form has convinced Pompey boss Danny Cowley to make enquiries into bringing the defender back.
With Rovers in the hunt for a new manager following news of Tony Mowbray’s impending departure, a decision on Carter’s future is not expected any time soon.
During his time at Ewood Park the central defender has made just 14 outings in Blue and White but has targeted a breakthrough at Blackburn following his recent loan stay.
The centre-back still has two years remaining on his current deal after penned fresh terms last summer following a successful spell at Burton.
Yet, with Blues fans learning what it could take to bring the centre-back back, they’d love to see an effort made to secure his return.
Here’s the best of the reaction from Twitter.
@dazza_nics: We paid more than that for the likes of Marquis & Harrison, no-brainer!
That’s like buying a Rolls Royce for the price of a Ford Fiesta!
@mattburnett23: £500k over a three to four year contract with use no doubt selling within two years if he kicks on is a no-brainer surely.
@DanKnight10: Is that it? That's surprising..... thought they'd want at least a million.
That figure is surely affordable after paying a lot more than that for Marquis.
@DawnRoberts1: Worth every penny... Get that pen out Danny!
@DDaveyDangerous: Absolutely bargain price. Absolutely will not find a player that good for that price. Half the price of John Marquis and a much better performer for us.
Absolutely no excuse not to try and pursue this and convince him to stay permanently.
@fireupthearcade: Considering we know what we’re getting this is a bargain! Be silly not to pay it. Seems to good to be true.
@pompeymad11: This would be a statement signing, fits the young player model and perfect for the team.
@Jake_PFC: That’s stupidly cheap, surely fits the model we’re going for too. Get that done.
@PFCOlly: Fits the model that the board have spoken about many many times, buy him; let him work his magic for two-three years and sell for significant profit.
Get it over the line Pompey.
@DanLewis1999: If we are serious about contending for anything competitive this season, just straight up pay that.