"Meghan should have known her father - who's sold stories to the press before - wouldn't keep the letter confidential". "It's not nice to talk badly about someone else just because you can, as he or she takes advantage of the anonymity of the web". "Please stop lying, please stop creating so much pain, please stop exploiting my relationship with my husband".
Thomas Markle Snr says the letter was sent by his daughter.
Kensington Palace is reportedly considering legal action over the leak.
"She told them both that the whole thing was becoming a nightmare, and that they should try and sort things out", the source said.
Last week, five unnamed people from Meghan's inner-circle opened up, wanting to "speak the truth" about the 37-year-old, after months of negative press and attacks on social media.
The Duchess' half-sister Samantha Markle has said her father is prepared to release more of the letter.
Many have drawn parallels between her relationship with Princess Diana and Meghan Markle's with Kate Middleton, with some going so far as to allude to it being the motivation behind her heartfelt letter.
Harry and Meghan watched a special performance of The Wider Earth, a critically acclaimed theatrical production about the young Charles Darwin's expedition on HMS Beagle.
This is in direct contradiction to what her father, Thomas Markle, has always claimed - that Meghan has shut him out of her life.
For instance, remember how her dad Thomas Markle spilled to the tabloids about his daughter?
"Women, in particular, are constantly pitted against and compared with each other in a way that reminds me of how people tried to portray Diana and me all the time as rivals, which is something neither of us ever really felt", Fergie wrote.