First Lady Melania Trump broke with long-standing tradition when she arrived at her husband’s State of the Union address alone.
Her office told reporters it was because she was accompanying White House special guests of honour.
But it has heightened speculation of a rift between her and President Donald Trump.
They have not been seen together since a report that he paid a porn star to keep quiet about their alleged affair.
Mr Trump denies an affair ever took place, but claims that he had paid Stormy Daniels $130,000 (£107,000) to remain silent over the alleged year-long extramarital liaison infuriated Mrs Trump, US media say.
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Both Barack Obama and George W Bush arrived with their wives for each State of the Union address they delivered – as did President Trump last year in his first speech to Congress.
But on Tuesday night, Mrs Trump arrived separately, to be greeted by warm applause as she accompanied special guests of honour.
She smiled and exchanged a wave with her husband as he appeared.
The first lady’s communication director, Stephanie Grisham, said Mrs Trump was not travelling with her husband because she was “honouring her guests for the true heroes they are”.
“In addition to holding a White House reception and photo opportunity for them, along with their friends and family, she is accompanying them to the Capitol,” Ms Grisham said in a statement.
“Once there, the first lady and [Second Lady Karen] Pence will host a more intimate meet-and-greet to engage with them on a personal level prior to the speech.”
However, that did not quell speculation that relations between Mrs Trump and her husband had soured.
Her choice of outfit also attracted attention, with some suggesting it was an allusion to the colour of choice of the women’s suffragette movement in the early 20th Century.