Rep. Steve King Steven (Steve) Arnold KingTrump, Biden deadlocked in Iowa: poll GOP leader: 'There is no place for QAnon in the Republican Party' Loomer win creates bigger problem for House GOP MORE (R-Iowa) took to Twitter early Thursday with a controversial claim about Texas Rep. Joaquin Castro Joaquin CastroFlorida Democrat asks FBI to investigate anti-Semitic, racist disinformation Hispanic Caucus members embark on 'virtual bus tour' with Biden campaign Hispanic caucus report takes stock of accomplishments with eye toward 2021 MORE (D) and his brother, former Secretary of Housing and Urban Development Julián Castro.

King said the two brothers, who are second-generation Mexican-Americans, took “Spanish lessons to qualify as retroactive Hispanics.”

Also two Texas politicians, Joaquin & Julian, the Castro twins, took Spanish lessons to qualify as retroactive Hispanics. https://t.co/W3qjfpxwHh — Steve King (@SteveKingIA) October 11, 2018

The GOP lawmaker’s remark came in response to a tweet criticizing Rep. Beto O’ Rourke (D-Texas) for changing his name from Robert Francis O’Rourke. The person who posted the tweet said it as “another example of just how Democrats get when the actual Latino in the race (Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE) stands against everything they stand for.”

The Castro brothers will reportedly join O'Rourke at stops along the Texas border as he seeks to unseat Sen. Ted Cruz (R) in the Texas Senate race.

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Julián Castro will also be joining former professional baseball player J.D. Scholten at two events in Iowa this weekend. Scholten is vying to unseat King in Iowa's 4th Congressional District in November's midterm election, Scholten's campaign confirmed to The Hill.

King has a history of making of making controversial claims on social media.

Late last year, King received widespread criticism for saying diversity is not America's strength.

Earlier this summer, King also prompted backlash for retweeting a message from Mark Collett, the former chairman of the youth division of the British National Party (BNP).

At the time, he said his retweeting of the prominent far-right British activist who has described himself as a "Nazi sympathizer” was “unintentional,” but wouldn’t say he was sorry for sharing the tweet.

-- Updated 6:20 p.m.