A retired teacher is facing jail over a Novichok hoax involving mystery bottles being found five times at Pembroke Castle in 2018.
John Ap Evans , 67, placed the bottles at the castle after the Salisbury poisonings.
Russian citizens Yulia and Sergei Skripal were poisoned by Novichok in Salisbury, Wiltshire, in March 2018.
Dawn Sturgess, 44, died months later after she came into contact with the nerve agent.
Police cordoned off areas of the ancient castle - where king Henry VII was born - after the bottles were found in a cavern behind the main building.
At least one of the bottles was labelled "novichok" when it was discovered in the grounds of the 11th Century castle.
Evans was due to stand trial but changed his plea to admit placing a substance or thing to induce belief that it is likely to be or contain a noxious substance or thing or create serious risk.The discovery of the bottles caused alarm and the castle had to be evacuated.Evans, of Northgate Street, Pembrokes, was later arrested after police set up a hidden camera.He is due to be sentenced at Swansea Crown Court next month.