Could certainly be.
The problem is I've asked the men who should know, the designers, and they can't remember. Imagine that, making 10s of thousands of miniatures over a 45 year period and not being able to recall when they made one knight figure?

Making my own supposition, I think it was either
a) Made for Citadel, but unreleased so passed to Foundry 'cus it's historical and the same bloke owned both companies,
b) Similar to above except it was a 'head-swop' of a Citadel model (as pointed out by Citizen Sade).