Is it possible to unshrink a jumper?

[Onlyconnect]

I have put DP's Paul Smith jumper in a machine hand wash and it's
shrunk. It looks quite funny but DP is not amused. Is there anything I can do about it?

No.
Sorry.

Nope. You could try pulling it. Doubt it'd work though. Soz.

It is time to turn it into a cushion. Reincarnation, woolly style.

One word answer: No.
Sorry.
I sympathise: I shrank a lovely jumper of DH's. Turned into a felted thing which might have fitted Thorin Oakenshield, but wasn't going to fit DH ever again.

no. which is why I did it to a particularly vile ex bf then weighted it down to stretch said jumper.
moo ha ha

I've read something online about wetting it, using lots of hair conditioner and carefully pulling it back into shape.
That obviously won't work if it's felted.