"In the past I have told them off for spending so much time away from their own people, that the people deserve more.
"Then, of course, I had to tell them, if they owe Tūhoe anything, they've repaid it 10 times back to the country through this contribution."
Shortland said he had spent a lot of time working as an apprentice under Kāretu and Milroy.
"We've all walked this road of language revitalisation, for many years.
"Every day someone who was a purveyor of the Māori language dies and with them go experiences you can't replace.
"Today Timoti and Wharehuia have left their works, their views, their standing on te reo and now we don't have to worry so much about losing their language in the future.
"It's always going to be there for us to follow and pursue."
He Kupu Tuku Iho will not be published in English and is intended for those truly immersed in Māori culture.
Milroy said they were blessed to have a launch on such a fine day.
"We hope what we've written will be of assistance for the generations to come, that they will benefit from what we've created."
He said the pair had maintained a good relationship during the writing process without any arguments.
"He would remind me of things that perhaps I missed out on and likewise I'd think about things he'd missed out.
"We have supported each other and have worked well with each other over many years."
Kāretu said the book was for the more "serious" te reo student.
"Let's hope this is an inspiration and its contents prove to be of interest and a functional addition to the Māori language."
