When asked if her father would be attending the pair's big day, she told 'The Wright Stuff': "Yes he is, God forbid unless a plane crashes through his roof, he'll be there one way or the other.
"So any rumour to the contrary is ... my favourite new word is becoming 'oh rubbish'. Yeah, so he will be there."
Samantha's comments come just days after Thomas praised Harry, 33, as a "gentleman".
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He said: "I'm very happy for them. I love my daughter very much - Harry's a gentleman."Thomas also insisted the pair's union is a "very good match".
The 73-year-old former lighting director added: "I think it's wonderful, I'm very delighted. I think they're a very good match."
In October last year, one month before Harry and Meghan confirmed their engagement, Samantha admitted she expected the pair to marry at some point but wasn't sure if she would be invited to the nuptials.
Samantha - who hasn't spoken to Meghan, 36, in nine years - said: "I don't know if I would be hurt, and out of love and respect I would go; of course I would go.
"We'll see if I get an invite."
Samantha also insisted her half-sister - whose dad is Caucasian and mother is African-American - wouldn't feel any pressure becoming the first bi-racial princess or duchess in British royal history.
When asked if her sibling might be affected by this, she said: "She is confident, not only in herself as a woman, but in her relationship with Harry and love that they have so that should speak for - and carry - them and everything else."
And that being said, it seems a non-issue."