Wills - what to do when the sole beneficiary has died??

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DUncle died over 5 years ago and his elderly widow (much loved paternal DAunt) is sadly in EOL care with dementia and not expected to last more than a day or two. I am executor/POA for them both as they had no children and their siblings (my late father and DUncs half sister) died over 15 years ago. DA&U had mirror wills leaving everything to each other. DAunt was unable to update her will after her husband died due to her dementia diagnosis.
What do we do about her estate (after care home fees paid) if the beneficiary (DUnc) has already died? Is it like dying intestate? DB, DSis and I are aunts only nieces/nephew and there are no other "cousins" alive. What questions should I ask her solicitor?
I've only just completed probate for DM and feeling really stressed about DAunts demise and another pile of admin looming 😪

Assuming she is in England/Wales, then the rules are here:

www.gov.uk/hmrc-internal-manuals/inheritance-tax-manual/ihtm12084

I am very unclear whether she is your blood relative or whether it was you uncle who was your father's brother?

Again for England/Wales, if the gift has lapsed (due to the death of the beneficiary) then the residue will form part of the intestate estate and be dealt with according to these rules:

www.gov.uk/inherits-someone-dies-without-will

If she was your father's sister then the estate would come to her siblings/their children.

But if she was your father's brother's wife, then the estate will go to her bloodline prescibed by the intestacy rules. This generally goes as far as cousins before it goes to the crown.

If Aunt's Will really does not provide what is to happen,then yes, the remainder of the estate-after payment of costs- has to be divided in the same way as it would be on Intestacy. The other terms of her Will still apply. Ask her solicitor who will be responsible for dealing with the estate and who will inherit. I'd take a family tree with you to your meeting. Mark it to show who has died.

Oh for an edit button. I didn't express that very well. Obviously the same rules of intestacy apply no matter whose relative she was. What I meant was if you are a blood relative it looks like you will inherit something. If you are not, I don't think you will.

Iknowitisheresomewhere - thanks for your response and apologies for not being clear. I've had little sleep over the last couple of nights and my brain is a mess!
DAunt is our late dad's sister. Based in England.