National Party Leader Bill English was not shocked when New Zealand First announced it had chosen to form a coalition with Labour, he told Morning Report.
"I wouldn't describe it as a shock, I think before the decision I kind of expected him to go with Labour and not us.
"Certainly there's been a strong reaction from the 44.5 percent of the country who voted for us."
He said he would not discuss what had tipped Mr Peters' likely choice nor whether National had offered him the deputy prime minister or foreign minister roles as those details fell under a confidentiality agreement around the negotiations.
Mr English is set to face his caucus for the first time since the NZ First-Labour coalition deal was announced last week.
While the future of Mr English's leadership will inevitably come up at this morning's meeting, National MPs will also likely be getting down to the business of Opposition.
Any challenge to his leadership of the National party would be a matter for discussion at the caucus, Mr English said.
"My feeling is they're more focused as a group on how to ensure that the huge gains made in this country can continue, and how to hold to account a government that's been put together in an unusual way."
The difference in views between New Zealand First and the Greens over a proposed marine sanctuary for the Kermadecs presents an early opportunity for National to harry the new government.
"We need to take into account the uniquely strong position of National going into opposition and the unusual if not weaker position of the government."
When asked how the new government was in a weaker position, he said it was because it "had not won the vote".
"When an election is lost, it's lost because a larger party captured the direction that New Zealand wants to go in.
"It's a legitimate result, but it poses unique challenges to the incoming government.
He would not say he thought National had a moral mandate to lead the country because of the result of the election, however.
"We accept like everybody else should, that it's a legitimate result of MMP.
"Some people really need success over the next two or three years, and part of our job is that of a uniquely strong opposition - bigger than Labour and New Zealand First put together.