Finland's Ambassador to the United States Mikko Hautala knows Vladimir Putin better than most diplomats. He has met him a dozen times, even in a sauna, he said, as he pointed to a photograph of him as the new Finnish Ambassador to Moscow presenting his credentials to Putin in November 2016, the day after President Trump was elected.

"Here I am with the Finnish president, we were actually flying to Sochi to meet Mr. Putin. That was in August 2014," Hautala said during an interview at his residence.

They were the first to meet with Putin after he invaded Crimea. Fox News asked him about the negotiations in the Russian sauna.

"I've been in lots of social situations with him yes," Hautala said in an interview with Fox News.

"In a banya?"

"I'm not going to comment on any specific, specific meetings, but yes I've seen him a lot."

Fox News asked him for his take on Putin now versus when he met him in 2014.

On the right is the Ambassador's grandmother, Laura Hautala, a member of Lotta Svärd, voluntary auxiliary paramilitary organization for women. She mostly served in air raid warning stations and was decorated several times. Here in the summer of 1943, during the Continuation War (1941-1944) against the Soviet Union. (Ambassador Hautala)

On the left is Hautala's grandfather, Veikko Hautala during the Winter War (February 1940) (Ambassador Hautala)

In the military service, summer 1992, right after the breakup of the Soviet Union. This shows Hautala as an Officer Candidate serving in Kainuu Brigade, located in Kajaani, NE Finland (Ambassador Hautala)

Hautala in Spring 1992 as an Officer Student, Reserve Officer School. Studying WWII fortifications on our Eastern border was part of the Program. (Ambassador Hautala)

In Kyiv, summer 2005. Visiting his Professor of Ukrainian language, Dr. Neonila Zaychenko. Hautala studied the language with her in 1997, 1998-2001. At that time most Ukrainians spoke Russian. Ukrainian was a rare language to study. (Ambassador Hautala)

After a tough marching competition in Reserve Officer School, April 1992. Hautala is standing on the right. (Ambassador Hautala)

Corporal Olavi Hautala, brother of Hautala's grandfather, was killed in action in July 1941. He was missing a few days and his grandfather felt anxious as they were fighting in the same platoon of 58 the Infantry Regiment. Hautala's youngest son at Olavi’s grave at the Teuva military cemetery. (Ambassador Hautala)

"I think he was during those times, bit more pragmatic. He wanted to listen, he wanted to understand the other viewpoints," Hautala who speaks fluent Russian and Ukrainian said. "What I see is that he's more ideological, more, kind of decisive, a bit less tolerant toward any different opinions. He has concluded that relations with the West are gone. There's not much to lose anymore."

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He arrived in Washington, D.C., to become Finland's ambassador to the U.S. in 2020, among the last group of ambassadors to present their papers to President Trump before COVID-19.

Fox News asked him why Finland now wants to join NATO.

He says the Russians should not be surprised that his country now wants to join NATO after Russia invaded Ukraine. He says he personally warned them in January this would happen if Russian troops crossed into Ukraine.

Last November, 20% of all Finns wanted to join NATO; now, nearly 80% want to join, according to recent polls, a dramatic shift in public sentiment after decades of neutrality after World War II.

"I think the major change of course was the Russian attack, because the popular mood started to change rapidly after that," Hautala said.

"The attack on Ukraine, which was totally illegal. It was unprovoked. I think it shocked the Finns in a profound way because they saw that their neighbor is really capable of such an action."

Russian President Vladimir Putin, left, and Finland's President Sauli Niinisto, right. (AP Photos)

Today as the Swedish Parliament debated whether to join NATO, the shift in tone from Vladimir Putin was as surprising as the decision of Finland and Sweden to apply to join NATO after decades of neutrality in the wake of Russia's invasion. Putin said unless NATO built bases in Sweden and Finland and put permanent troops there, Russia would not have a problem with Finland and Sweden joining NATO.

"As far as expansion - new members Finland and Sweden included - Russia - I would like to remind you, dear colleagues - doesn't have any problem with those countries," Putin said to six former Soviet States marking the 30th Anniversary of the Collective Security Treaty Organization. "Therefore, there is not an immediate threat to Russia with the inclusion of those countries. But the expansion of military infrastructure over that territory will obviously call for our response."

Some Russian spokesmen have threatened to deploy nuclear weapons to Finland’s border if Finland joins NATO. Today Putin responded with a more subdued and nuanced warning.

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Finland's President called Putin Saturday to tell him that his country planned to join NATO after decades of neutrality.

"In my opinion, the NATO membership is an act of peace, it's about war never returning to Finland," Finnish Prime Minister Sanna Marin told Parliament.

Sweden’s Prime Minister Magdalena Andersson told Parliament:

"Should Sweden be the only country in the Baltic Sea region that was not a member of NATO, we would be in a very vulnerable position, we can't rule out that Russia would then increase pressure on Sweden."

Finland’s Ambassador to the U.S. said of Russia’s response: "They have always said that they would react in some way. Most likely they will place more military resources close to the Finnish border."

"Nuclear weapons," Fox News asked?

"I don't see that as a kind of a major issue here," Hautala said.

"Finland has a large number of nuclear bunkers. Are you preparing those bunkers," I ask.

"They have been built and prepared and they stay ready."

Unlike most pending applications to NATO, the ambassador says Finland would not be a drain financially to the alliance.

"We fulfill all the criteria that you can imagine. We are a well established democracy. We are among the best rule of law countries. We are the least corrupted country in the world," Hautala said. "We have never dismantled our armed services. Finland brings more resources, they will bring added value to the alliance.

We have a lot a lot of military capabilities in relation to our size."

Finland is already spending more than 2 percent of its GDP on defense, unlike many NATO members.

"We have a large army. We have a modern Air Force. I think one of the best in Europe. We have a huge artillery. I think it can be even the biggest one after Russia. It's really, it's really strong. 76% of our population is ready to defend our country militarily, regardless of the outcome."

Some of the ambassador's most sensitive, and classified discussions with other diplomats and American officials take place in his sauna in northwest Washington, D.C., where frank discussions can be had and there is no place to hide listening devices. This is where he makes his opponents sweat, he joked as he showed Fox News his sauna. At the entrance is a photograph of the father of modern Finland General Carl Gustaf Emil Mannerheim.

Hautala spent his formative years as a young diplomat in Ukraine - he is fluent in Russian and Ukrainian. "I basically fell in love with the place." He recalls a particular evening in early 2000 when one Friday evening at a restaurant on a main street in Kyiv, he was packed into a restaurant with other Ukrainians. "Suddenly, there was a silence. Total silence. A man came in with the Russian Ministry of Interior camouflage uniform. So he had a Russian flag and a Russian emblem. I noticed the people went silent. And everybody was looking at that guy." Hautala added he took a mental note: "People started to stare. And I sort of made a mental note that this country is developing kind of an identity a sense of its own."

The Finnish ambassador grew up with the stories of his grandfather, a Finnish farmer, deployed to the trenches on the border with Russia fighting the Russian invasion of Finland in 1939 at the start of World War II during what became known as the Winter War. It was 45 degrees below zero Fahrenheit. The Finns pushed the Russians back and the Russians signed a ceasefire after three months.

"They were farmers, just ordinary people. They were very patriotic," Hautala said. "One of the myths in Russia about Finland is that we used to have snipers in trees."

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The Ambassador still has his grandfather's diary describing how the Finnish citizens armed to the teeth waited in the forests to attack the invading Russian troops.

"Finland was 4 million; Soviet Union was almost 200 million," Hautala said. "So the difference was huge. But I think what basically saved us was that the fact that we had more motivation like we see now in Ukraine."