'It's time to man up': Meghan Markle's sister blasts Prince Harry

Britain's Prince Harry and Meghan Markle attend a reception for the Commonwealth Youth Forum at the Queen Elizabeth II Conference Centre, London. Photo / AP

Meghan Markle's estranged half sister Samantha has taken aim at Prince Harry in another Twitter rant ahead of the Royal Wedding.

Samantha Grant, who has the same father as the actress, attempted to tell the Prince to "man up" via the social media site, the Daily Mail reported.

The 53-year-old questioned Harry's humanitarian work and accused him of being a hypocrite by 'allowing Meg to ignore the Markles'.

Her tweet came as Meghan was embarking on her first major event on behalf of the Royal Family today when she joined Prince Harry for a Commonwealth reception in London.

She wrote: "It's time to 'man up' @HRHHenryWindsor. 'Shout outs' about humanitarianism, don't work when you are allowing Meg to ignore the Markles. It is s (sic) contradiction.

"Someone must point out that the 'Emperor is not wearing any clothes'."

However the account she was directing the message at is not actually the Prince, but a fan account pretending to be him.

Grant, who uses a wheelchair after being diagnosed with multiple sclerosis, also uploaded two new profile pictures of herself a week after changing her image to a photo of her and Meghan in their childhood and at graduation.

She has previously accused the actress and Prince Harry of "inviting complete strangers" instead of her relatives and says her half-sister and Harry are failing to honour "proper etiquette and tradition".

Last week Grant said Meghan must do the "morally right thing" and invite her entire family to the Windsor event on May 19.

Last week Grant uploaded a profile picture of Meghan Markle with her at her graduation. Photo / via Twitter

She said: "Closeness has nothing to do with it, it is incumbent upon her to do the morally right thing and invite family and demonstrate she has a ­humanitarian heart."

She added: "Smoke and mirrors cannot hide the elephant in the room. Out of respect, tradition and humanitarianism, the #Markles should be invited if 2,000 complete strangers are invited.

"Our uncle who got her the internship, brother, me, best friend of 30 years Nikki Priddy, nephews. Fact."

Britain's Prince Harry and his fiancee Meghan Markle arrive at the Queen Elizabeth II Centre during the Commonwealth Heads of Government Meeting. Photo / AP

Meghan's half-sister appears to be left off the guest list along with her brother Thomas Markle Jr, his ex-wife Tracy and their children Thomas and Tyler Dooley.

Today Meghan met youth delegates taking part in this week's high-profile Commonwealth Heads of Government Meeting (Chogm) in London.

It is unusual for someone who has not yet married into the royal family to be involved in a high-profile occasion such as the Chogm summit.

But the Queen, who is Head of the Commonwealth, has made clear she sees Harry and his future bride as lynchpins of her work with the so-called "family of nations".

Markle attends a reception with Harry for the Commonwealth Youth Forum. Photo / AP

Markle, 36, who has given up her acting career to devote herself to being a full-time royal, has no previous links to the Commonwealth, but has worked with the UN as a women's advocate for Political Participation and Leadership and undertaken several humanitarian missions.

Grant has also confirmed she is writing a book about her half-sister.

In the past, she claimed to have raised Meghan for 12 years when she was growing up in California.

But other sources speculate that the pair had little to do with one another.

The Palace announced last Wednesday that world leaders and politicians would not be included on the list of those attending the wedding.

US President Donald Trump, UK Prime Minister Theresa May and the Obamas have not been invited to the wedding.

But they invited an extra 1200 members of the public to the castle for the celebrations as reward for their community work.