Thomas Markle has warned that 'everything will come out' if he faces daughter Meghan in court.
The Duchess of Sussex is suing a newspaper for publishing a personal letter she sent to him in August 2018.
Mr Markle has already agreed to be a witness and pledged to expose what he said were 'lies' about him.
'It will be emotional. I don't know how we will both accept it,' he said.
'It would be the worst place to have to meet her and Harry - but it might come down to that because I will certainly testify against the things that have been said about me. The lies.'
Thomas Markle, appearing in a Channel 5 documentary that aired last week, has warned that 'everything will come out' if he faces daughter Meghan in court
Mr Markle, Doria and their daughter as she started her career and within a few years of this photo she would be earing $40,000 per episode of Suits
Mr Markle also called the Sussexes' decision to step back from their duties the 'dumbest thing'.
Labelling Prince Harry 'whipped', he also told the Sun his daughter 'has turned into his mother'.
The two have not spoken since the fall out before the Royal wedding in 2018, with Mr Markle yet to meet Prince Harry or grandson Archie.
He revealed he had gone to the Mail on Sunday - the sister paper of the Daily Mail - about the infamous letter in order to defend himself from attacks from Meghan's friends in People magazine.
Meghan, 38, has accused the newspaper of breaching her privacy, her data protection rights and her copyright when it published extracts.
The 75-year-old has already given lawyers previously unseen text messages that reveal the breakdown of the relationship between father and daughter.
Mr Markle also called the Sussexes' (pictured) decision to step back from their duties the 'dumbest thing'
Thomas Markle said he knew Meghan would be a star after seeing her perform as a teenager
Mr Markle added: 'I'm tired of being lied about and not being defended.
'I put the newspaper in this position by offering up a portion of that letter, which led to them being sued.
'This is my fault so I have to stand up for myself. It is a responsibility thing.'
In the letter, Meghan allegedly accused her father of breaking her heart 'into a million pieces' and causing her to 'crumble inside' by colluding with a paparazzi photographer.
Mr Markle, however, said the Sussexes had done 'exactly what they told me I shouldn't be doing' by stepping back.
He added: 'They are cashing in on the Sussex name.
'They've gone commercial. They should be just called Harry and Meghan now.
Mr Markle showing some royal souvenirs he keeps on the mantle of his home during the Channel 5 documentary that aired last week
'Leaving the Royal Family is the dumbest