West Australian MP Peter Abetz, brother of Senator Eric Abetz, says his reaction was "mixed" when he first learned his great uncle was a convicted Nazi war criminal.

Otto Abetz was Hitler's ambassador to occupied France and convicted in 1949 of crimes that included deporting French Jews to the death camps.

Speaking on SBS's Insight program (transcript here), Peter Abetz, who was elected to the WA Legislative Assembly in 2008, twice insisted his great uncle had also done "positive things".

"I think it was one of mixed reaction in that he did some really positive things but he also did participate in, you know, the deportation of the Jews which is really, there's no excuse for that whatsoever and yet he also did some very positive things," Abetz said after host Jenny Brockie asked how he felt when he discovered the family's Nazi past.

"I was told that he - when the Americans were advancing on Paris - because he was so passionate about French culture, he actually negotiated with the Americans to, and the Wehrmacht, that the Germans would vacate Paris and not booby trap anything if the Americans gave them I think three or four days to withdraw and the French were incredibly grateful for that because that way Paris wasn't actually destroyed."

During Abetz's trial by a French military tribunal one witness, a high-ranking Nazi official, claimed Abetz, who was passionate about French art and architecture, was instrumental in disobeying Hitler's order to raze Paris in 1944.

Quizzed by Brockie on whether he tried to "cling to the positive" about his notorious relative, Peter Abetz said he had been deeply touched by a visit to the Holocaust memorial in Israel.

"I found that a very, very moving experience and the horror of thinking that, you know, I had a great uncle who was actually involved in that horror," he said.

Leichhardt councillor Darcy Byrne was among some people who took Abetz to task on social media over his responses.

Unbelievable! Peter Abetz (Western Australian Liberal MP) and brother of Eric Abetz (far right wing Abbott Government...Posted by Darcy Byrne on  Tuesday, 4 August 2015

Abetz also has a family connection to Field Marshal Erwin Rommel who was a cousin to his mother's father.

Abetz said Rommel was an "interesting character".

"I understand he was the only high-ranking general in the German Army who refused to join the Nazi party," he said, adding that his mother was "quite positive and proud about that aspect of his legacy".

Later, Abetz admitted that Rommel was an admirer of Hitler but also pointed out he had been part of a plot to remove the Nazi leader in 1944.

After a 12-day trial Otto Abetz was sentenced to 20 years' hard labour by the French court.

However, Abetz was freed in 1954 by French president Rene Coty. Four years later, he and his French wife were killed in a head-on collision on the autobahn near Dusseldorf.

Insight: Bloodlines part 2 airs next Tuesday 11 August featuring relatives of Harry Truman, Hideki Tojo, Weary Dunlop and others on SBS