Actor Robert Downey Jr. and his wife, Susan, have welcomed a baby girl, according to People magazine.

The couple's new daughter joins their family, which consists of the couple's two-year-old son, Exton Elias, and 21-year-old son, Indio, whom Downey fathered in a previous marriage with Deborah Falconer.

Last week at the BAFTA Los Angeles Jaguar Britannia Awards, the "Iron Man" actor gave a tribute to his pregnant wife and then-unborn daughter in his acceptance speech after receiving the Stanley Kubrick Britannia Award for Excellence in Film.

"It's just the uncertainty of how nowadays you have all these things where you think you have much more of an understanding of what you're going to get," Downey said in his speech Thursday. "And then this little soul lets herself be known to you, and it's just like: You don't know anything. It's great!"

The 49-year-old then asked his wife, "who is literally about to pop," to stand up and be recognized by the crowd.

"How is she still so darn pretty and functional and mood-stable?" he jokingly remarked.

Downey then dryly added that "the second pregnancy has been extraordinarily tough for me."

"Self-prescribed mandatory bed rest was of some benefit. At least my milk is finally coming in," he added.

The producer, 40, and the "The Judge" star have been married since August 2005. They announced their expected arrival via Twitter in July.

Following the reveal, Downey told E! News that he didn't "know what really prepares a dad" because this would be his first daughter.

"I'm asking around, but I did my part and now I'm just going to show up and do what I'm told," he said.

Over the past several months, the couple has been busy promoting "The Judge," their first joint movie project. Unfortunately, just as the press tour was starting, Downey's 80-year-old mother, Elsie Ann Downey, passed away.

Downey's rep has not publicly commented on the birth.