Carl Sargeant revealed allegations of bullying in the Welsh Government to a Conservative AM three years ago, the Senedd has heard.
In a dramatic statement, Darren Millar said he submitted questions to First Minister Carwyn Jones about bullying in 2014, at the Labour minister's request.
Mr Sargeant was found dead four days after being sacked from the cabinet.
The Welsh Government said Mr Jones stood by his previous answers on the matter.
Clwyd West AM Mr Millar said on Tuesday he felt a "moral obligation" to speak out. One AM, who was in the chamber at the time of the statement, said members were visibly shocked.
Mr Millar said he had a private conversation with Mr Sargeant in October 2014 when the late minister said he was "unhappy because there was bullying going on within the Welsh Government which was coming from an individual in the First Minister's office".
This was "taking a toll on him personally along with others", Mr Millar said.
The Tory AM said he would not name the individual - Mr Millar stated that Mr Sargeant never accused the first minister Carwyn Jones of bullying.
Two weeks later, in the assembly members' tea room, Mr Sargeant gave him a hand-written note containing draft questions to submit to Carwyn Jones.
Mr Miller said he re-drafted the questions and showed them to Mr Sargeant before tabling them.
"His only motivation in disclosing the problems in the Welsh Government to me and requesting my support in this way was to attempt to resolve the frustration and stress of the ongoing situation at that time for him and his colleagues in the Welsh Government," Mr Millar said.
Mr Sargeant, who was the AM for Alyn and Deeside, acted out of loyalty to the government and Labour, he added.
At the time, Mr Millar asked whether the first minister had ever received any reports or been made aware of allegations of bullying by advisers to the government.
The first minister replied that no allegations were made - an answer that "surprised and disappointed" Mr Sargeant, Mr Millar said.
Analysis by Mark Palmer, BBC Wales political unit
This was a dramatic moment that left some assembly members visibly shocked.
AMs are often seen working on their Senedd computers as debates continue in front of them - but not on this occasion.
Those present sat up and listened as Mr Millar delivered what was billed as a "personal statement".
Some had an inkling of what it was all about, but they weren't expecting him to go into such detail.
One AM said he saw others leave the chamber in tears.
The first minister wasn't there to hear Mr Millar.
The 2014 questions resurfaced following Mr Sargeant's death in November, with Mr Jones saying: "Any issues that were brought to my attention at that time were dealt with."
Those answers are now the subject of an investigation into whether Mr Jones misled the assembly.
An independent adviser - former lawyer James Hamilton - will publish a report into whether the First Minister broke the ministerial code.
Ministers who do so are expected to resign.
Mr Millar has said he wants to provide evidence to the Hamilton investigation.
A Welsh Government spokeswoman said: "The first minister stands by his previous answers on this matter and has already encouraged people to provide any relevant evidence to the independent advisor."