While he has respect for his former coachs abilities, Biggar has revealed he had a sometimes fraught relationship with the 61-year-old New Zealander during his playing days.

"I have the utmost respect for Gats as a coach, what he has achieved with Wales, what we achieved together," Biggar added on BBC Radio Wales.

"The relationship with Warren was professional, it wasn't an overly warm one.

"It was one of mutual respect. I just felt on a couple of occasions we could have done things better."

The relationship with Gatland is one of the subjects Biggar covers in his new autobiography.

The fly-half has highlighted incidents such as when the Wales squad threatened to strike for the 2023 Six Nations game against England over player contractual issues.

While acknowledging Gatland was in a difficult position because he was a Welsh Rugby Union (WRU) employee, Biggar accused the coach of siding with the governing body during its dispute with players and expressed frustrations at the final outcome.

Biggar also criticised Gatland for a newspaper column the coach wrote after a World Cup warm-up game in August 2023.

Gatland's column criticised Biggar for having an argument with Owen Farrell at Twickenham after the England's captain high tackle on Taine Basham, which resulted in a red card for the home skipper. Biggar admitted Gatland's column had first left him angry and later disappointed.

Biggar also stated that at one point in 2023 he wondered whether Gatland was the coach he had once been, although he conceded Wales' progress to the last eight of the World Cup had justified his reappointment by the WRU.

"I am the first to say I am not an angel or easy to manage," Biggar told the Scrum V podcast.

"We are both stubborn and didn't help each other in that sense, but it's one of those things.

"There will be bits in the book people will read but it's important to highlight Warren's CV as a coach, it's important to note we were very successful under him.

"His first time in Wales, he changed the Welsh rugby landscape and made Wales into what we were.

"Now we are disappointed we can't quite get back there at the minute."