Pop star Kevin Jonas was "a wreck" when he witnessed his two-year-old daughter meeting her newborn sister for the first time.

The former Jonas Brothers musician became a father for the second time in October (16), when his wife Danielle gave birth to a girl named Valentina.

Kevin has now opened up about life with his little ladies, revealing he was an emotional mess the moment Alena was introduced to her baby sibling.

"I think I was more of a wreck than anyone else," the 29-year-old confessed to People.com. "It definitely became very real 'cause you're in the moment, you're obviously going through labor and she has the baby and it's euphoric and awesome. And then reality strikes (sic) in when your other one walks in the door."

Danielle admits she also struggled to keep her emotions in check, having just given birth: "I was crying and I was trying to hold it in because I didn't want Alena to get scared because there's no reason to be scared."

The sisters' first meeting went well and the new mom feels "blessed" Alena has fallen in love with Valentina, but it hasn't been a completely smooth transition for the parents themselves.

"It's been definitely crazy and a learning curve," she shared. "It feels like you have five kids when you have two because you're juggling. But (it feels) very, very good."

The couple celebrated its seventh wedding anniversary on Monday (19Dec16) and Kevin is still in awe at how well Danielle has managed to adjust to their busy family life.

"Dani gives so much of herself, it is insane," he gushed. "She works herself to the bone. She's up till two o'clock every morning and up at seven, six, or whatever and multiple through the night. But then she finds ways to give time for both and make them both feel so special, even though there's two. And even time for me!"

Kevin and Danielle are now looking forward to spending their first Christmas together as a family of four, and the guitarist admits having a few extra people around the house when their relatives arrive will be a big help.

He said, "(We're) just keeping it low key. We're gonna be with the families and just relax. It's actually complicated because everybody pines for time (with the kids)...! Everybody can come live with us when we have the kids because we can be like, 'Here you go!'"