Aly Michalka is a first-time mum.

The Aly & AJ musician and actress revealed to People on Monday that she and her husband Stephen Ringer welcomed their son, Jack Francis, into the world on 21 April, two weeks before her due date.

"It was a very peaceful and calm birth, which is really what we were hoping for," Aly, 35, told the outlet. "He's just a great little guy. He's got a really special disposition about him."

After 50 hours of labour, including six hours of active labour, Aly gave birth to Jack at their home in Santa Barbara, California with the support of Stephen, a midwife and two doulas.

"It was just wonderful. It was really everything we could imagine it would be," she added of the birth. "We just kind of knew immediately like, 'Oh yeah, he's a Jack.'"

The couple named their son after Aly's late grandfather, while Francis is a Ringer family name.

After relaxing in bed with Jack for the first week, the Potential Breakup Song hitmaker returned to the studio to continue making the next Aly & AJ album with her sister.

"He took to the change really well. He was very much a little chameleon in that sense, and I think we got lucky with the fact that he didn't have really any major sleep issues," the Easy A actress said about bringing Jack along to the studio.

Aly started dating film producer Stephen in 2013 and they tied the knot in 2015.