JJ Watt of the Houston Texans makes a 6 year old's day by "marrying" her.

A 6-year-old's woeful YouTube video about not being old enough to marry Houston Texans defensive lineman JJ Watt lead to a surprise proposal, complete with a Ring Pop ring, a white jersey wedding gown and a first dance to Justin Bieber.

"It first started when we saw on the news that JJ Watt was having a hard time finding a good girlfriend because of his fame and everything," Lindsey Bartay, mother of the mournful Breanna in the YouTube video, told ABCNews.com. "He wanted to make sure he had the right one."

"I called her in because she loves him," Bartay said. "I said, 'Breanna, come look, he's looking for a good girlfriend,' and she came in and she's like, 'Yay, I'm going to marry JJ Watt. He's so awesome. I love him.'"

But Breanna's grandmother was in the room and told the little girl she had to be at least 25 to get married.

"And then she started just boo-hooing, just really, really hard crying," said Bartay.

In the video, a tearful Breanna says, "I just want to marry JJ Watt."

"I'm not old enough," she cries. "I wish my birthday was in like ... what is his birthday?"

Bartay said she wanted to send the video to relatives, but it was too big for an email or a text, so she posted it on YouTube on Jan. 12. It has been viewed more than 300,000 times.

About two weeks later, the video made its way to Watt, who tweeted, "Does anyone happen to know this cute little girl? We have to find her and turn those tears into a smile."

"After a little while, people started emailing and calling, saying, 'JJ Watt is looking for you,'" Bartay said.

Bartay said she received some negative comments from people saying she was trying to get something from Watt by posting the video, so when he finally called and said he wanted to meet Breanna, Bartay was initially reluctant.

"But he was like, 'No, no. I really want to do it for her,'" Bartay recalled.

Watt wanted to surprise his young fan, so he set up a tour of the Houston Texans Reliant Stadium for her. When Breanna asked her mom if Watt would be there, Bartay said that he couldn't be there because he had an early flight and wouldn't be able to make it.

Breanna was disappointed but thrilled to see the giant photos of Watt in the stadium. A tour guide walked the family through the gift shop, and a surprise was waiting in the next room.

"When we walked through the next room, he was down on one knee with the Ring Pop in his hand and he said, 'Breanna, come here,'" Bartay said.

At first, Breanna thought Watt was a statue, saying to her mother, "He looks so real."

"Then she walked over to him and he said, 'I know we can't really get married, but would you be my pretend wife for the day? And she said yes," Bartay recalled with a laugh. "Then he said, 'Thank goodness. I didn't know what I was going to do if you said no. I was so nervous. I've never fake proposed before.'"

He gave her a bouquet of flowers and put on his own candy ring. He presented Breanna with a white version of his 99 jersey, which was floor length on her, to serve as her wedding gown.

Watt showed the family around Reliant Stadium, and then stopped to remind Breanna that they hadn't had their first dance yet. He asked her if she liked Justin Bieber -- she did -- and they danced to "As Long as You Love Me."

"They danced to the entire song," Bartay said. "He twirled her around and kind of spun himself around and tried to dip her. She was so shy.

"At the very end, he said, 'I love you,' and she said, 'I love you too,'" Bartay said. "Not only is JJ a class act, but what amazing parents he has to have raised such a fine, caring young man. I thank them."