A Patagonian woman was sent back to her home country after British immigration officials refused to believe she was travelling to Wales to learn Welsh.
Evelyn Talcadrini, from Puerto Madryn, Argentina, was on her way to Glyndyfrdwy, near Llangollen, to spend six months living with a local family to practise her Welsh.
But she was put on a flight back to South America within hours of landing in the UK.
Now the Government has agreed to launch an investigation into her treatment after Plaid Cymru's Hywel Williams and Elfyn Llwyd raised the case in the House of Commons during Welsh questions.
Mr Williams, Caernarfon MP, said: "She travelled for 35 hours to get to Heathrow, but was summarily ejected and sent back. She is not the only young Welsh Patagonian who has, unfortunately, suffered summary ejection for no good cause that I can see."
The MP said it was a "disgraceful stain on our welcome to Welsh Patagonians."
Some 20,000 Welsh people settled in Patagonia in the mid-19th century because they wanted to keep their language and religion at at time when English was becoming the predominant tongue. The first group sailed aboard the Mimosa from Liverpool in May 1865.
Evelyn had been due to spend her time in Wales with Eos Griffiths and his Patagonian-born wife Carina at their home in Glyndyfrdwy, and showed a letter from them to the immigration officials at Heathrow.
Mr Griffiths said: "I have known her family for more than 30 years and invited her to stay with us. I thought she would be able to improve her Welsh and learn some English and enjoy the Eisteddfod at Bala this summer."
Wales minister Wayne David said the United Kingdom welcomed Patagonians who were keen to explore their Welsh heritage.
"Of course the UK Borders Agency does not have any separate policy in relation to Welsh-speaking people from Patagonia. I give my commitment that the Secretary of State and I will meet the relevant Home Office Minister as soon as possible."