The 23 year old was the product of a one-night stand Wagner had with a dancer friend and he had no idea the baby had been put up for adoption until it was too late.
The actor had given up all hope of ever meeting his love child, whose name is Kerry, when she showed up backstage at a concert in Florida in November (11).
Recalling the moment he met the girl during an appearance on Access Hollywood Live, the choked up actor said, "In rushes this amazing young girl, crying... She stayed for the show, we spent the next five days together on this cruise I was supposed to be a part of and we got to know one another and caught up and she's amazing."
Wagner confessed he never doubted the girl's story - or her ties to him: "When she held me, it was just so powerful - and I knew."
The actor admits he had some explaining to do to his sons, aged 21 and 17, when he got home.
He added, "Now they have a sister... They tried to get it but it was a process explaining the truth of it. Once they met her I think that actual connection... made it a little easier for them, and now they text and Facebook."
Wagner's daughter will be in Los Angeles later this month (Mar12) to cheer her father on when he competes on U.S. TV show Dancing With the Stars.