Conan O'Brien let the stork out of the bag Monday night – by congratulating Liev Schreiber for expecting a baby with Naomi Watts.
"Yes, I'm going to be a dad," Schreiber said in response to the announcement by the Late Night
host. "Very exciting."
Before that, the couple had been officially mum on the subject. However, a publicist for the Escada fashion house, which designed Watts's Oscar gown, revealed the news
Sunday in a press release. It read, in part, "The ESCADA gown set off her most precious new asset – the baby she is expecting with longtime boyfriend Liev Schreiber."
Schreiber jokingly told O'Brien that he "gave grief" to Watts – whom he described as "normally a wallflower" – for her suddenly being so sociable and going to the Oscars. (Schreiber, meanwhile was back on the East Coast during Oscar night, as he is starring in the Broadway revival of Talk Radio
"And she said, 'No, no – it's a very auspicious thing that our embryo is going to be at the Oscars,' " said Schreiber.
When it comes to selecting a name for the child, "I'm trying to stay out of it all," he adds. "I'm trying not to make any decisions, [because] everything that I try to do in service of her or the coming baby is wrong. So I really don't even go to my house much anymore."
One thing for sure, however: The baby will not be named Liev. "It's an awful name," said Schreiber. "It's probably the most oft-mispronounced name in showbiz."
Watts, 38, who starred in King Kong
, and the Manchurian Candidate
leading man, 39, started dating in 2005 and were first seen in public at a U2 concert in Manhattan on May 21 of that year.
Watts's pal, Australian designer Jayson Brunsdon, recently told PEOPLE that the actress "will be a great mum. She is the kind of person that looks after you."
On the screen, the parents-to-be recently starred together in The Painted Veil
. Up next, Watts stars in the thriller Eastern Promises,
while Schreiber appears in a film adaptation of the book Love in the Time of Cholera.
As for starring together in a real-life wedding, both Watts and Schreiber have not mentioned the subject publicly, though last June, while promoting his movie The Omen
, Schreiber set the record straight about a 5-carat ring that he had reportedly bought Watts. "That is Naomi's," he told PEOPLE. "She has some jewelry of mine but not that."