GRoB in property. Valuation discount not available?

Think I’m clutching at straws here but…

H&W settle their house into Trust but still live in it so a GRoB. H now died. With other failed PETs and GRoB, leads to IHT liability of just over £4K. Am I right that the 10% joint property discount is not available on the GRoB as spouse still in the property (and house in the Trust?)