"In the year 2050, I will be 56 years old. Yet right now the average age of this 52nd Parliament is 49 years old," Swarbrick said before dropping an "OK boomer" when she was heckled by Muller before continuing.
A "boomer" is shorthand for a baby boomer - someone born between 1946 and 1964.
While Swarbrick's "OK boomer" insult went global, the jibe was misdirected - Muller is only 52, making him a Generation X baby.
Muller has a political history.
He was a staff member of former prime minister Jim Bolger and always touted to be a successful politician, with Bolger now backing Muller to take over from Simon Bridges.
Muller chose to go into the private sector after working for Bolger.
He went to Parliament in 2014 after working at Fonterra.
Muller took a significant paycut to make a run in Bay of Plenty, a safe National seat.
In 2017, he rose up the party ranks and was tasked with holding the climate change portfolio.
On Wednesday, Muller confirmed he would contest National's leadership.
He sent a letter to all National MPs, advising them of his decision to contest the leadership. An emergency caucus meeting will be held at midday tomorrow.
"It is essential that National wins this election," Muller wrote.
"I share the view of the majority of my colleagues that this is not possible under the current leadership."
Muller said the country faced the most enormous challenge since the end of World War II.
"Labour has failed to deliver on every measure it has set for itself in Government. This will not change and the consequences of it being re-elected at this time will be catastrophic for two generations," he wrote.
"Our communities and our economy are at stake. It is essential National wins this election."
