US Congressman Tony Gonzales has admitted to having an extra-marital affair with an aide, having previously denied that the relationship happened.

The Texas Republican, who is married with six children, said the relationship with married staff member Regina Santos-Aviles, who died by suicide last year, was a "mistake" and a "lapse in judgement".

"I take full responsibility for my actions," Gonzales, 45, told a podcast.

His admission came hours after a House of Representatives panel launched an ethics investigation into the relationship, and ahead of a primary run-off election. Gonzales had previously dismissed the allegations as "blackmail" and a "coordinated" attack to unseat him.

The primary race to decide whether Gonzales can remain as the congressional district's Republican candidate is headed to a May run-off after neither Gonzales nor rival Brandon Herrera crossed the 50% vote threshold earlier this week.

Whoever becomes the party's nominee will stand in November's midterm election. The district, which runs along the US-Mexico border, is heavily Republican.

Gonzales was endorsed by US President Donald Trump before the affair allegations surfaced.

The lawmaker is now facing growing calls for his resignation, including from fellow Republicans. Among them are South Carolina Congresswoman Nancy Mace, who has accused him of "predatory behaviour".

Santos-Aviles died in September 2025, after setting herself on fire near her home in Uvalde, Texas. The medical examiner ruled her death a suicide, according to the BBC's US partner CBS News.

In an interview released on Wednesday, Gonzales told conservative podcaster Joe Pags that Santos-Aviles' death had nothing to do with the affair, saying she was "thriving" at work.

"I had absolutely nothing to do with her tragic passing," he said. "And in fact, I was shocked just as much as everyone else."

The House Ethics Committee announced on Wednesday it was launching an investigation into whether Gonzales "engaged in sexual misconduct" towards one of his employees.

The panel will also examine whether he discriminated unfairly by "dispensing special favours or privileges".

In Wednesday's podcast interview, Gonzales said he did not reward Santos-Aviles more than other constituency staff.

A pay rise that she received was part of a "staff-wide pay increase", he said.

Gonzales said "there's a whole lot more to the story", without offering details. The BBC has contacted his office for comment.

"When you make mistakes like this, you know, it's never easy," Gonzales told the podcaster Pags. "It humbles you."

"I've asked God to forgive me, which he has," he added.

According to CBS, in explicit text messages from May 2024, Gonzales asked Santos-Aviles to send him a "sexy pic".

The aide, who was his regional district director in Uvalde, reportedly told him twice that he had gone "too far".

The following month, Santos-Aviles's husband, Adrian Aviles, appeared to send a text from her phone to Gonzales and other aides that said he had discovered "she's been having an affair on me with your boss Tony Gonzales for some time now".

In a recent interview with CBS, a lawyer for Aviles said that Santos-Aviles' mental health sharply declined following the end of her alleged relationship with the congressman.

"The deterioration of her mental state was exacerbated by the conduct Tony engaged in - the workplace harassment after the discovery of the affair," said the lawyer, Bobby Barrera.