Labour MP Ann Clwyd is to give evidence the Assembly health committee today, as part of a wider review of patients' complaints about Welsh hospitals.
The Cynon Valley MP complained about the conditions her late husband endured before he died at the University Hospital of Wales in Cardiff.
She went on to carry out a review of hospitals in England for the UK Government.
Previous attempts by opposition parties to invite Ms Clwyd to give evidence at the Senedd were blocked by Labour AMs. They said it was 'constitutionally inappropriate' to invite a backbench MP from Westminster.
The decision was later overturned.
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The Talyllyn runs from Tywyn, near Aberdovey, for more than seven miles to two villages in the south Gwynedd countryside.
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