One of the patients who died after contracting an infection at the hospital complex was 10-year-old Milly Main.
Milly’s mother, Kimberly Darroch, said the news “confirms” what she and other bereaved families had feared.
She said: “We thought that political pressure was applied to open the hospital before it was ready, and now we know the truth – that’s exactly what happened.
“The denials about this in recent days have added to our pain and anguish – we were lied to, and this proves it.
“We are edging closer to the truth, but we still don’t have the full story. Milly would not want me to give up until the truth was uncovered and I will not.”
The inquiry will publish a full report and recommendations at a later date, though there is no set deadline.