"Clearly the fern is the symbol. I'll vote for the flag which has blue and black."
"There are very few flags around the world that have the Union Jack stuck in the corner recognising they are part of the former British Empire - colonial cousins as it were. So [it's] time for change."
In his capacity as chancellor of Waikato University, Mr Bolger, 80, an avowed republican, led the trade delegation accompanying Mr Key to Vietnam.
He has stayed active since being ousted as Prime Minister by Jenny Shipley in 1997, first as ambassador to the United States, then as chairman of New Zealand Post. He has remained involved in the Treaty of Waitangi settlements process, which was initiated under his leadership, and became chancellor in 2007.
He is occasionally a special envoy of Mr Key and spent time lobbying countries of central Asia and much of the former Soviet Union for New Zealand's successful bid for a Security Council seat. He also represented Mr Key at a summit of the Asia-Europe (Asem) meeting in Milan.
"There were 50 prime ministers, presidents and me."
As Prime Minister, Mr Bolger opened New Zealand's embassy in Hanoi about 20 years ago and an office in Ho Chi Minh City.
"It's great to be back and see the progress the country has made."