'Big Bang Theory' 's Johnny Galecki Reveals Special Message He Sent to Unborn Son in Series Finale

Michael Yarish/CBS Leonard (Johnny Galecki) and Penny (Kaley Cuoco) on The Big Bang Theory

Johnny Galecki gave a sweet nod to his baby boy on the way in the series finale of The Big Bang Theory.

In Jessica Radloff's oral history book The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, Galecki shared that the season finale where his and Kaley Cuoco's characters (Leonard and Penny) reveal they're expecting a baby together was actually "mirroring" his own life at the time.

The actor, 47, noted that when filming the finale, he and his then-girlfriend Alaina Meyer were expecting their first baby together.

"That was mirroring what my life was at that point, too, with my hand on Kaley's stomach in the last scene of the show," Galecki shared in Radloff's book. "That was a little something for my son, [Avery] Orbison, who wasn't born yet, to see a little later in his life."

"I asked Kaley if it was OK if I did that, and she smiled at me, knowing exactly why I was doing that, because that's a little salute to him that will be forever," he added.

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Cuoco said filming the final scene of the CBS sitcom was special for her as well.

"To then end it like that, [this time] sitting next to Leonard and him touching Penny's stomach… it was the perfect cap," she shared. "I wouldn't have wanted it any other way."

Galecki and Meyer announced in December 2019 that they had welcomed their first baby together, son Avery. The former couple first went public with their relationship in September 2018 and announced their baby on the way in May 2019.

In November 2020, a source told PEOPLE that Galecki and Meyer had split and were co-parenting their son Avery.

Galecki previously dated Cuoco, his former Big Bang Theory costar, for two years before breaking things off in 2010.

The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series is available now everywhere books are sold.