WASHINGTON (NYTIMES, REUTERS) - Hope Hicks, the White House communications director and one of President Donald Trump's longest-serving advisers, said on Wednesday (Feb 28) that she was resigning.

Hicks, 29, a former model who joined Trump's 2016 presidential campaign without any experience in politics, became known as one of the few aides who understood his personality and style and could challenge the president to change his views.

Hicks had been considering leaving for several months. She told colleagues that she had accomplished what she felt she could with a job that made her one of the most powerful people in Washington, and that there would never be a perfect moment to leave, according to White House aides.

Her resignation came a day after she testified for eight hours before the House Intelligence Committee, telling the panel that in her job, she had occasionally been required to tell white lies but had never lied about anything connected to the investigation into Russia's interference in the 2016 election.

She did not say what her next job would be, and her departure date was unclear, but it is likely to be in the next few weeks.

Hicks said that she had "no words" to express her gratitude to the president, who responded with his own statement.

"Hope is outstanding and has done great work for the last three years," Trump said. "She is as smart and thoughtful as they come, a truly great person. I will miss having her by my side, but when she approached me about pursuing other opportunities, I totally understood. I am sure we will work together again in the future."

Hicks was caught up in a controversy surrounding former White House staff secretary Rob Porter, another close Trump aide, whom Hicks had been dating. She worked to defend him when charges of domestic abuse against his two former wives emerged. Porter was ultimately forced to resign.

As communications director, Hicks worked to stabilise, to some extent, a fractious press department of about 40 people who were often at odds with one another in 2017. She maintained one of the lowest public profiles of anyone to ever hold the job, declining to sit for interviews or appear at the White House briefing room podium.

"I quickly realised what so many have learned about Hope: She is strategic, poised and wise beyond her years," said John F. Kelly, the White House chief of staff.

"She became a trusted adviser and counselor, and did a tremendous job overseeing the communications for the president's agenda including the passage of historic tax reform. She has served her country with great distinction. To say that she will be missed is an understatement."