The lecturer taught Charles how to say a few words in Welsh before his investiture as Prince of Wales in 1969. In an eulogy, his daughter described the retired Aberystwyth University teacher as a proud Welsh nationalist, an academic and campaigner.
Dr Millward’s teachings were shown on an episode of The Crown entitled Tywysog Cymru, which means Prince of Wales in Welsh, with Dr Millward played by Mark Lewis Jones.
In one of his last interviews Dr Milward explained how he warmed to the 20-year-old prince during their hour-long lectures at Aberystwyth University.
Dr Millward said: “I was not in favour of him becoming the Prince of Wales but I didn’t argue the point with him.
“I got on quite well with him, he was good to get to know.
“I found him intelligent and quite charming, we stayed in touch for a long time afterwards.”
Dr Millward said many of the scenes in the TV series never happened including a moment in which that he invited the student to his home for tea.
He said: “That wouldn’t have happened because my wife Sylvia was not in favour of him.”
In Netflix’s The Crown, the teenage Charles is shown a photograph of the Welsh village where Tedi and Sylvia met along with a claim it was flooded to become a reservoir supplying water to England.
Dr Millward said: “That didn’t happen either, I don’t know where they got that from.
“They didn’t consult me before making the film although I did meet the actor who pays me and he was very nice.”
The TV series portrayed Prince Charles giving Dr Millward a book of English tongue-twisters to get his own back over his struggles with learning Welsh.
Special Branch police thoroughly audited Dr Millward before he was designated as Charles’s Welsh teacher.
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He was a leading Welsh nationalist and had come close to being arrested during a Welsh language protest in 1963, six years before the Prince’s controversial investiture at Caernarfon Castle.
The university lecturer said: “The police had me in their black book so I was bit surprised when I was asked to teach him Welsh. The police interviewed me very sternly.
“When I met him I tried to be neutral, I just treated him the same as any other student.
“I’m not particularly proud of being his Welsh teacher, it was forced upon me.”
Prince Charles stayed in touch with Dr Millward, who would give him advice if he had to make an address in Welsh during his engagements in Wales.
Dr Millward’s daughter Llio Millward said in a statement: “I think firstly of my father as a nationalist.
“His passion towards the Welsh language and culture drove every aspect of him, from his personal life, as an academic and as a campaigner.
“He was very unassuming and I had to nag him to write his autobiography.
“But you could see he was, as the Welsh Language Society’s former leader Jamie Bevan said in the foreword, one of the quiet giants of our language and our culture.”