No invite? Big problem!

Samantha Grant still hasn't received an invitation to half-sister Meghan Markle's May wedding to Prince Harry, 33, and she has some feelings about it.

So she gave her sister, 36 -- from whom she's been estranged for years -- a piece of her mind in an epic rant on her private Twitter account on April 11, MailOnline reported.

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"The Markle family is looking forward to our wedding invites. No one has one yet. Still waiting," she tweeted, kicking things off. "I hope London is wheelchair friendly. Excited!" (Samantha, who's 17 years older than Meghan -- with whom she shares a father -- is a former actress who suffers from multiple sclerosis and is wheelchair-bound.)

About an hour later, Samantha shared more of her feelings.

"At issue is not a matter of closeness as more than 1000 complete strangers are invited. Family is family I have an uncle I have only seen once but I would never say he is not family because we are not close. Humanitarians move forward with love and kindness especially to Family," she wrote.

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It's worth noting that the wedding venue, St. George's Chapel at Windsor Castle, holds about 800 people, according to reports. Though "Entertainment Tonight" has reported that fewer than that, about 600 guests, have been invited to attend the actual ceremony on May 19 as well as a lunchtime reception to follow that will be hosted by Queen Elizabeth II.

Just 200 guests are being invited to a separate evening reception at nearby Frogmore House that's being hosted by the groom's father, Prince Charles.

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"Smoke and mirrors cannot hide the elephant in the room. Out of respect, tradition, and humanitarianism, the #Markles should be invited if 2000 complete strangers are invited," Samantha added another hour later . "Our uncle who got her the internship, brother, me, best friend of 30 years Nikki Priddy, nephews. Fact."

Like Samantha, who's repeatedly spoken to the media -- often to share comments that are critical of her younger sister -- Meghan's childhood pal Nikki has also publicly discussed her history with Meghan, which royal watchers believe is exactly why they are not being invited.

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In February, Meghan's former brother-in-law -- Samantha's ex-husband, Scott Rasmussen -- publicly warned Meghan not to invite Samantha.

"Harry and Meghan need to know the truth about her. She's the last person who should be at Windsor Castle," Scott, 59, told The Mirror. "In my opinion, if she sets foot in the UK, they should send her straight to the Tower of London... She should act with some dignity, keep her mouth shut, and leave everybody else alone."

He claims Samantha has said unkind things about Meghan because she is envious of her little sister's success in life.