"He was a very overpowering personality, his presence seemed to cause certain responses," says Frank Sinatra Jr of his legendary musician father.
We are sitting in a small, dark room in London's Savoy hotel, the late Frank Sinatra's favourite place to stay in the English capital. And yet his son is not feeling nostalgic or emotional about returning for the first time in more than two decades.
"They have changed this hotel rather severely and it's not the same," he says gruffly.
It's not just the hotel that has changed, Frank Sinatra Jr is also not the same boy who first made international headlines in 1963, when he was kidnapped at the age of 19 and held ransom until his father coughed up $240,000 (about $1,832,000 in 2013 dollars). He - the younger brother of singer and actress Nancy Sinatra - is now 69 and working on behalf of his father's legacy.
Like his father, he sounds like an American straight out of a Jazz age movie, and boasts a polite but direct demeanour. However, you wouldn't guess this man comes from one of the most famous showbiz families of all time.
"I haven't looked at a music chart in 35 years," he says honestly. It's then I realise I am speaking with a man whose musical interests remain firmly in days gone by.
A pianist, songwriter and "student of music" himself, Frank Jr is most passionate when talking about the industry but has very little respect for the way it is run now.
"Music is all but non-existent now. Today it is created and performed by a whole plethora of amateurs. Be grateful that when you get sick and go to the doctors that they don't allow amateurs to perform medical appliance on you with the same degree of mediocracy that music makers have today," he says, without the smallest flicker of humour.
It makes sense, then, that the reason for our meeting is not for a new musical project but for the re-release of Frank Sinatra's 1993 'Duets' album, which saw the King of the Hill end his career top of the heap.
'Duets' sold over three million copies in the United States alone; unprecedented for an artist of Frank's age in a musical landscape that was dominated by rock and rap. The record saw huge names such as Anita Baker, Tony Bennett, Bono, Natalie Cole, Gloria Estefan, Aretha Franklin, Liza Minnelli, Carly Simon, Barbra Streisand, and Luther Vandross sing with Frank, arguably starting the trend of superstar duets.
It's been 20 years since the album first came out and, although Frank Jr says he's not qualified to say what has changed in terms of his father's legacy, he does comment: "It pleases me that Frank Sinatra's music still has an audience, because many people who have come into the music world and then passed out of the music world are long since forgotten. He has been able to enjoy this great longevity."
Why re-release it now? "It is because of the new association with Universal Music, they're very excited about it. I just hope that their excitement is justified," he says.
Frank Jr himself appeared on the 'Duets II' album. However despite being "delighted" to be asked to sing with his father, he says the collaboration "was wrong".
"The idea of the duets albums was the people who joined Frank Sinatra in each song were themselves successful record artists, I never was. I felt a certain apprehension at the time that some people thought my being there was pure nepotism. I felt kind of out of place about that," he explains, giving an honest insight into what it must be like to be the son of someone so enduringly distinctive and beloved.
I ask Frank Jr if he's been happy with his own musical career so far, and he simply replies "sometimes" in a way that suggests a man who has not had his own dreams completely fulfilled.
"I have to do what I have to do like everyone does. I didn't know anything else, I had to do what I felt I had some talent in doing."
Despite not feeling comfortable duetting with is father, Frank Jr did go on to work with the 'My Way' singer after placing his own career on hold and becoming Frank Sr's Musical Director in 1988.
"He said 'why don't you come out and conduct for me?' and I was very surprised because he had much better musicians available to him than I ever was," he says modestly.
"I'm glad I did it because as the years went on - I was his Musical Director just a little bit less than seven years - it suddenly became very clear to me why it was important to be there for him.
"When I joined him he was already in his early seventies and as the years went by he was gaining on 80 and he needed my help. This was a professional relationship, the companionship did occur but that wasn't part of the equation.
"It was important that I tried to be of help."
Since his death 15 years ago, Frank Sr's music is not the only thing that is still spoken about. His personal life continues to be scrutinised, with his ex wife Mia Farrow last month suggesting, in a Vanity Fair interview, the possibility that her son Ronan's father might be Frank Sinatra and not Woody Allen - who was long considered to be Ronan's biological father.
Does his father's legacy have a price to pay when it comes to intrusions into his personal life?
"I don't know, now you're asking me to define an element of human nature and I don't think I'm qualified to do that. There are those people today who still enjoy the music and performance of Frank Sinatra, therefore they are familiar with his personality and his life," he says, making it clear where the boundaries lie.
That's not to say Frank Jr won't give an insight into the type of man his father really was. He previously said he had "every strength and every weakness a man could have". But says those strengths and weakness are too many to list.
"Let's just say this was not a person who could ever be accused of being a saint and this was not a person who could ever be accused of being a devil either...
"He was honest in what it was that he was… he rather disliked deception and I don't blame him. Of course performing is something different, what is done by a performer on stage is called an act but life is not an act and this is the way he looked at it."
Finally I ask, what was the most important thing that his father - one of the best selling artists of all time - taught him about life?
"The thing that he taught me was truth. He said to me one time there is no good or bad truth, there is only truth. And I think what he was trying to say was, through life let us be objective and we'll save ourselves a lot of unnecessary detouring and inconvenience."
Frank Jr may not have eclipsed his father's career or legacy but, from our encounter, I can tell he is one man that is not afraid of honesty.
Frank Sinatra: Sinatra Duets - Twentieth Anniversary is released on 18 November, 2013, bringing together the original Duets and the follow-up Duets II, remastered with special extras.