The source describes the most recent developments as "an increasingly desperate situation" with the options being for an intermediary to intervene on Meghan's behalf, or for the 37-year-old to cut her father off permanently.
PA Wire/PA Images The Duchess of Sussex talks to fellow guests as they arrive to attend the wedding of Charlie van Straubenzee and Daisy Jenks at St. Mary the Virgin Church in Frensham, Surrey.
The Duchess rocked a shirt-dress from Club Monaco (which you can get here) and a hat by Philip Treacy.
Now she's taken to Twitter to accuse Meghan of neglecting their father - by refusing to send him a birthday card.
For the most part, Meghan Markle's life has been going great.
Tiger Woods shoots 73 to close WGC-Bridgestone Invitational
That fact must have been on his mind after a lethargic performance in the third round of the WGC-Bridgestone Invitational. You just don't know if they're ever going to see me win if I don't win here, so it was pretty cool to get it done".
Happy birthday, Meghan Markle! The couple will also attend the opening of the 2018 Invictus Games in Sydney, following their public coming out at the Toronto Invictus Games previous year. Or perhaps the Duchess will be able to reach out to her dad to try and heal the rift.
It has already been announced both Harry and Meghan will attend.
So is it to do with royal protocol, or is the former actress taking fashion pointers from her sister-in-law?
"For someone to say you should turn down a paycheck...tell your boss that you don't want a paycheck".
The royal couple, holding hands, left together shortly after the hour-long ceremony ended and sped off before the newlyweds were showered with confetti.
"I think, you know, one step at a time", he said.