The celebrities came out for Bradley Cooper and his pregnant girlfriend Irina Shayk's back-to-back birthdays.

On Thursday, Jan. 5, the actor turned 42. On Friday, Jan. 6, his lady love celebrated her 31st birthday. E! News reports that the duo celebrated on Thursday night with a slew of celebrity friends, including Alyssa Milano and husband David Bugliari, Aaron Taylor-Johnson and wife director Sam Taylor-Johnson, Sienna Miller, Dave Chappelle, Jonah Hill and Lady Gaga.

Prior to the festivities, a source told E! that Bradley had "something very special planned for Irina's birthday."

The source added, "He already got her some very thoughtful gifts and some of the gifts might just even sparkle."

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Jonah, who starred in "War Dogs" with Bradley, was the first to arrive at the Pacific Palisades home near Los Angeles. He left before guests sang "Happy Birthday."

Gaga arrived and even performed inside the home on the piano. David also exercised his musical bone, playing the saxophone. He left around midnight and was the last to leave.

On Friday, Irina shared an image of a multi-tiered cake with mandarin oranges to Instagram.

Thank U everyone for the bday wishesπŸ˜˜β€πŸŽ‚πŸŽˆ

A post shared by irinashayk (@irinashayk) on

"Thank U everyone for the bday wishesπŸ˜˜β€πŸŽ‚πŸŽˆ," she captioned the snap.

The joint birthday marks the end of an era for the duo -- they will be parents by the time their next birthdays roll around.

In late November it was reported that the duo was expecting a little one.

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An insider told E! at the time that Irina, who has dated Bradley for nearly two years, was in her second trimester and is "so excited" about becoming a mother for the very first time. It will be Bradley's first child, as well.

"Bradley been really supportive and helpful towards Irina. They both can't wait to have a baby," a source said. "Bradley been really busy with work and running around back and forth but Irina and him are in constant contact. She is such a cool women and lets him have his space when he needs to work, etc."

Another source had said in December that the two have already picked a few baby names they like and that they know the sex of their child.

"Bradley and Irina love each other so much and this is not gonna be the only kid," the second source said, "there will be a few more after this one."