Thomas Markle claims he heard about Duchess of Sussex's pregnancy on the radio

Meghan Markle's estranged father claims he found out he would be a grandfather when he heard the Royal Baby pregnancy news on the radio.

Already grandfather to five before the arrival of Archie Mountbatten, whom he's yet to meet, Thomas Markle the 74-year-old says it sounds like "a joke" when he tells others how he discovered his daughter was pregnant.

"I was sitting in my car waiting to cross the border and I heard the good news from the royals is that Meghan is pregnant," he claims in a new documentary Thomas Markle: My Story, to air Wednesday night in the UK.

"Which is almost a joke when you tell people, well you heard it on the radio.

"This is my daughter, talking about my grandchild. She's going to have a grandchild that's mine. I'm not hearing about it on the phone, I'm hearing about it on the radio."

Markle appears in a 90-minute tell-all interview, filmed last October over six days in his home in Mexico, in which he details his experiences of his daughter's wedding and pregnancy, according to The Mirror newspaper.

He describes not being part of this chapter in his daughter's life as "kind of painful" as talks about their feud, which is only likely to be reignited following the new TV appearance.

The Duke and Duchess of Sussex famously announced they were expecting their first child just hours after landing in Australia for the start of their first overseas tour together as newlyweds in October 2018.

They spent 16 days travelling across Australia, New Zealand, Fiji, and Tonga beginning with the Invictus Games in Sydney.