Strahan will be ending his four-year run with Ripa on Live! to join Good Morning America as a full time co-anchor in September and a source tells PEOPLE Ripa "was completely blindsided."
"It all happened very quickly," adds the source.
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"She's a no-show today. No quote from her anywhere wishing him well," says the source. "She was pissed two years ago when he was asked to do just two days a week on GMA."
A rep for Live! tells PEOPLE Ripa "had the day off today," and the star was replaced by Ana Gasteyer, who came out with Strahan to a cheering crowd.
"Yes, I am leaving this show," confirmed Strahan. "I'm going to go over to GMA full-time. Which is going to happen in September. And it's the same channel!"
He also addressed some of the reactions over the announcement.
"I was reading some stuff and it was like I died!" he said incredulously.
"But I do want to say to all of our viewers out there … four years ago when I came here I'm sure they were surprised," he said, joking about being the guy with the "gap tooth."
"You still continue to give us your eyeballs and watch this show. Thank you guys. I couldn't have asked for better fans at all," he went on. "You guys are absolutely amazing."
Strahan, 44, also reassured viewers he's "not going anywhere."
"I'm always available to guest co-host because I consider myself to be a part of this family forever," he said.
"We've still got months to go," he added. "You better not start crying, you're going to make me cry!"
At the end of the program, Strahan also took a moment to thank Ripa.
"I really want to thank, of course, Kelly Ripa," he said. "Kelly welcomed me here and I've learned so much from her. She's just been an amazing influence on me and this has truly changed my life to be here with her."
"And I know that the show will continue to be strong and great because of Kelly ... and the staff here because everybody here is so talented," he added. "This show has not been around for over 30 years by mistake."
"Kelly, I thank you. I love you and everyone else here at Live!, and I'm not going to cry on TV momma, I promise you," he concluded.
The former NFL pro first joined the GMA team in 2014, appearing twice a week while co-hosting Live! at the same time.
Live! With Kelly and Michael airs weekdays (check local listings).