White House communications director Hope Hicks, one of the president's longest and most loyal advisers dating back to the beginning of his presidential campaign, said Wednesday she is resigning from the administration to explore new opportunities.

“There are no words to adequately express my gratitude to President Trump,” Hicks said in a statement. “I wish the president and his administration the very best as he continues to lead our country.”

A former model, Hicks, 29, is Trump’s longest serving aide, having worked with him before he announced his candidacy, through the campaign and into the second year of his administration.

“Hope is outstanding and has done great work for the last three years,” Trump said in a statement provided by the White House. “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 informed the president on Wednesday that she had made her final decision to leave the administration, a source said. Hicks’ exact departure is to be determined but will be sometime in the next few weeks, the White House said.

“Hope Hicks is loved & admired by all who know her,” the president’s daughter and adviser, Ivanka Trump, tweeted. “It’s with a heavy heart, but tremendous gratitude, that I wish her well in her next steps.”

The announcement came a day after Hicks acknowledged to a House intelligence panel that she occasionally told "white lies" for Trump but has not lied about anything relevant to the Russia investigation.

Hicks joined the White House after the campaign, and was promoted to communications director over the summer. The White House credited her with leading strategic messaging for the tax reform effort and working with White House Press Secretary Sarah Sanders to stabilize the press and communications teams.

“When I became chief of staff, I quickly realized what so many have learned about Hope – she is strategic, poised and wise beyond her years,” chief of staff John Kelly said in a statement.

Kelly added: “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.”

Hicks famously avoided publicity throughout her tenure. As a press aide, she never went on camera but preferred working behind the scenes. It wasn’t until recently – during the scandal over White House Staff Secretary Rob Porter’s past domestic abuse allegations – that Hicks found herself in the spotlight.

At the time of the scandal, Hicks had been dating Porter, who has also resigned. It was then revealed that Hicks was involved in drafting the initial response to the revelation of Porter’s past.

Sanders told reporters Wednesday afternoon that Hicks already had considered leaving the administration before the Porter fiasco.

"She's been thinking about it before that," Sanders said.

She also said Hicks' resignation did not have to do with her testimony before the House Intelligence Committee.

Hicks also has been of interest to investigators in Special Counsel Robert Mueller’s probe over her involvement in drafting the statement after news broke of Trump’s eldest son, Donald Trump, Jr., meeting with a Russian lawyer who promised dirt on Hillary Clinton during the campaign. Hicks was with the president on Air Force One while they were writing the initial statement.

The White House has had trouble keeping someone in the communications director role. Jason Miller initially was chosen for the job, but ultimately turned it down citing family reasons.

Mike Dubke briefly served in the role but resigned in May after just three months on the job. Anthony Scaramucci resigned from the role in July after just 11 days on the job after Kelly became chief of staff.

Hicks stepped into the role after Scaramucci’s departure.

“Hope Hicks is a world class person and is going to go on to have an unbelievable career. She did an incredible job,” Scaramucci tweeted Wednesday. “The best is yet to come.”

There was no immediate word on her successor.

Fox News' Serafin Gomez contributed to this report. The Associated Press also contributed to this report.