Welsh First Minister Carwyn Jones says he had "no alternative" but to sack former Cabinet Secretary Carl Sargeant.
He promised doing "all that I could to make sure everything was being done by the book" when allegations of groping were first made against Mr Sargeant.
The former minister for children and communities was found dead on Tuesday after being sacked and suspended by the Labour party. It is understood he took his own life.
Mr Sargeant's family said he was not afforded "common courtesy, decency or natural justice" when reports first surfaced of "certain incidents".
But speaking in Cardiff, Mr Jones defended his actions and hailed his former colleague as a "force of nature".
"Wales has lost a person of great warmth, ability and charisma," he said.
"These are the darkest days that any of us can remember in this institution – but they are darkest of all for the family."
Mr Jones called Mr Sargeant "my friend", and said the pair had never argued in 14 years of knowing each other.
He added there was "great hurt, anger and bewilderment" over the events, and welcomed a "legal process" that would scrutinise his own actions.
But the First Minister defied a call from Neil Hamilton, the leader of UKIP Wales, to resign.
After his death, Mr Sargeant's family released correspondence showing he was facing allegations of "unwanted attention, inappropriate touching or groping". The 49-year-old, a married father of two, had denied the claims.
According to a letter sent to Labour on Monday, Mr Sargeant's solicitor had demanded immediate details of the claims, along with the names of complainants.
The correspondence revealed there was an anticipated hearing date of 16 January, while the solicitor added the "ongoing delay" of Mr Sargeant learning details of the allegations was "both prejudicial to the preparation of our client's case but also to his physical and mental wellbeing".
A Labour party spokesperson said: "Following allegations brought to the attention of Welsh Labour by Welsh First Minister Carwyn Jones, an investigation was launched by the UK Party.
"The Labour Party governance and legal unit spoke with Carl Sargeant and, in line with agreed procedure, outlined the nature of the allegations that had been received and how the complaints process works."